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Old 07-26-2019, 09:41 PM
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Angry Chasing an erratic idle, P0505...

Good evening WF,

I wanted to throw out my situation with an idle issue and associated P0505 code (IAC valve and/or circuitry).

I've been chasing this issue for 6 weeks now, largely with the help of this forum and the gurus (Jerry - ). At this point I'm near to calling the PCM the faulty link, but - as I hate to throw expensive parts at a component I haven't fully bench tested - I'd like to reignite a popular thread here with the permission of the court. I have indeed gleaned this forum and the associated others for as much info as I can find. Therefore, this will (respectfully) be more of a recap of a troubleshooting process to hopefully find the last bit of advice I need to solve this, and maybe help some others in the process.


The subject:

- 2002 Wrangler 4 liter, 5-speed AX-15 (Terminator from RSG)
- Banks turbo (important to note: PCM has indeed been flashed/overwritten due to the Banks setup; no issues with 4 years on the setup)
- 234k miles, sole owner, good compression, negligible oil seepage


The problem:

6 weeks ago, the idle speed went erratic and code P0505 popped, indicating an issue with the IAC and/or associated circuitry.


Symptoms:

1) While in neutral with the throttle plate closed (hot or cold), the idle won't maintain a typical ~700 RPM. All too often, when shifting into neutral while coming to a stop, the idle speed drops immediately and kills the engine. This is indicative of the IAC being fully closed and not reacting to a closed throttle condition (inputs from the TPS). Similarly, when the engine is behaving as such, letting off on the throttle while in gear produces a noticeably increased amount of compression braking, further indicating a fully-closed IAC valve. In these cases - am I to allow the Jeep to roll to a stop - it rolls to a complete and dead stop, engine and all.

Though, half of the time on a hot or cold engine, these symptoms don't exist at all, despite the P0505 code. (?)

2) Occasionally, on a hot engine, the idle will instead climb incrementally while in neutral or in gear, topping out around 2000 RPM, before slowly (and incrementally) slowing back down to typical idle speed.

The incremental change in engine speed is important to note, as the increments occur quickly in ~200 RPM steps. This suggests that the PCM is in fact controlling the IAC, and that the IAC is at least responding to inputs, regardless of their accuracy. A significant vacuum leak wouldn't produce such incremental and noticeable "steps" in RPM.

3) Throughout every 100 miles of driving, the P0505 code will generally extinguish, and the Jeep will run fine. Then - only upon a restart (hot or cold) - the code will trip again.

4) When acting up, throttle response is sluggish and dirty at speeds <1200 RPM. The motor seems completely happy once it's up to speed (>1200 RPM), regardless of the code being set.


What's been tested so far:

1) Upon smoking the intake manifold, a substantial amount of smoke was visible around the throttle plate shaft. I therefore (had the justification [IMG]file:///C:/Users/lathamj1/AppData/Local/Temp/msohtmlclip1/01/clip_image002.gif[/IMG]) to replace the original TB with a new 62mm BBK. Wonderful change in low-end throttle response...no change in idle symptoms at hand. (I.e., TB is also completely clean.)

2) Slaved in a spare IAC valve; problem persists. Slaved in a new (aftermarket) IAC valve; problem persists. Through researching the operation of the IAC valve through various pubs, this forum, and the Jeep FSM, I validated continuity of both internal coils of each IAC valve along with proper (expected) resistance. Therefore: IAC valve(s) are not considered to be the problem.

3) Verified wiring from each of 4 pins at the IAC connector back to the corresponding PCM connector for both stray voltage and resistance; all check good under ignition on/off conditions. Unwrapped harness; no visible breaks or abrasions between IAC connector and PCM. Therefore: wiring is not considered to be faulty or sporadically grounding out.

4) Using a digital multimeter (i.e. not analog - important to note) I have a strange - possibly oscillating - 12VDC signal at the IAC connector, across all 4 pins to ground. This doesn't seem correct, though perhaps it would make sense if the PCM was actively trying to adjust the IAC valve with the connector removed. (Maybe?)

I haven’t the knowledge currently and have yet to find a good resource to properly test the incoming IAC voltage signals.

I was under the impression that only 2 of the 4 pins would have a 12VDC signal (outer pins), with the remaining 2 pins being grounded. This voltage is controlled solely by the PCM. Therefore, this condition is considered suspect.

5) There is a small exhaust leak at the #1 exhaust port. It is audible under operation, but minimal. (This "could" be the problem, but other symptoms suggest otherwise, I'm thinking.) This is next on the list to repair, but not currently considered to be suspect.

6) No leaks at the head gasket are suspected due to oil/coolant quality and lack of contamination/other evidence of a head gasket leak, along with good compression.

7) The TPS registers a smooth and linear idle condition of 16.9% up to ~80%, with the idle voltage/percentage "believed" to be in range of acceptable idle voltage feedback. I need to research this further to verify that 16.9% isn't too high a feedback voltage while at idle, though I recall reading that the PCM should adjust its baseline values to account for TPS changes and that 16.9% "should" be just fine. Therefore: the TPS is not considered suspect at this point, though further verification is ultimately necessary.

8) When engaging the AC compressor, the IAC valve seems to always function, regardless of current RPM. I.e., there is always an obvious – or at least a subtle – indication that the IAC valve has opened just a hair for the compressor. Even when the engine is limping along at ~200 RPM, engaging the AC will not kill it or even affect the engine speed.

As an aside, this strikes me as odd; I was under the impression that a minimum RPM had to be registered to engage the AC clutch. (?) I need to confirm that the compressor is actually engaging at very low RPMs; consequently, this on the list. Regardless, at normal RPMs, the IAC is in fact properly compensating for AC compressor load.


Weird things I've seen in the last year:

1) Twice in the past year, the instrument cluster has gone nuts for all of 5 seconds on each occasion, with the fuel gauge dropping to zero and the speedometer cycling (quickly) between "top speed" and zero. I don't recall the tach ever responding as such during these moments. This is indicative of a PCM problem, as individual sensor failures would affect only single gauges.

2) Last week, the fuel gauge moved itself to ~1/2 tank and stuck there for half an hour before returning to a normal (expected) reading. This occurred immediately after swapping in LED bulbs in all corners (without resistors.) Soon after, the problem corrected itself, inexplicably.

3) Fuel economy has been steady, despite a welcomed and constant increase ~3 months ago as ethanol requirements in fuel finally disappeared.

4) The oil pressure reads ~40 psi when the ignition is on without the engine running; pressure climbs to ~80 psi when the engine is running, suggesting an oil pressure sender issue. Slaving in an aftermarket (borrowed) unit confirmed ~40 psi at operational RPM a year ago. This is on the list to swap out and fix, as the swapped sender wasn’t a keeper. (For now, 80 psi = 40 psi, and movement throughout RPM changes is foolishly acceptable for me as proof that oil pressure exists.)


All in all, these symptoms are erratic, but consistently erratic at this point, and seem to fluctuate between "existent" and "non-existent" throughout ~10 minute intervals. I.e., sometimes she’s behaving, and sometimes she’s not.

I don’t like throwing expensive parts at something without reason, and – with a respectable background in technical troubleshooting – I’m quite desperate for a concrete reason to replace the PCM, especially considering that this Jeep continues to be my dependable daily driver for over 17 years now.

Any and all insight would be appreciated. And…thank you to all those who take the time out of their lives to read this ~1400 word communiqué.

P.S. This Jeep has seen a shop one time – under warranty – when the AC died prematurely at 28k in 2004. This was and shall be the only time it sees a dealership!


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Old 07-27-2019, 05:13 PM   #2
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You have certainly done your homework.

Testing the PCM output seems to be something that the FSM does not clearly address.

First, I know the PCM reflash was long before this started happening but will ask who did the reflash, Banks?

Second, here is something I found that may be helpful (some you have already done) & the source link if you need more info but think this is probably the important part in testing the IAC & wiring. Unpinning the 4 wires at the PCM is explained & might be particularly helpful.

I know you have run the wires but also know there bolt sticking through the firewall from the cab behind the engine which is a known place that can damage the harness & hard to see. I don’t know if those wires run back there but if so worth rechecking.

https://www.obd-codes.com/p0505


This should be a fairly straightforward diagnosis. Start by clearing the fault codes. Then unplug the IAC and start the engine (This may cause other IAC codes to set. Just ignore them for now). If the P0505 code doesn't reset, replace the IAC. It is internally shorting one of the IAC circuits. If the code DOES return after unplugging the IAC and starting the engine, then you know it isn't the IAC motor. Visually check the wiring harness all the way back to the PCM. You may need to visually inspect the harness by removing all the insulation off the wires. It is possible that the wires could be shorting to each other or to other wires in the harness. If there are no wiring problems, and the code keeps returning with the IAC unplugged, you can check the PCM by removing the IAC wires from the PCM connector (or clipping the wires in a location where they can be repaired easily) and then start the engine (If you're not sure, don't do it. Take it to a qualified professional). Now if the code doesn't reset there is a problem with the wiring. Check for continuity on all the IAC wires. Any resistance points to a problem. Check for voltage on any(At this point there shouldn't be any voltages on the wires because they're clipped at one end and unplugged at the IAC). Repair as necessary. But if the P0505 code DOES reset after removing the IAC wires from the PCM connector (or clipping them), replace the PCM, there's a problem internally on the IAC control circuit.



Lastly, here is from the FSM which you have referred to indicating you have it but note there are 2 potentially significant things to note. One is the reference to 2000 RPM & the other to the MAP sensor & its part in the IAC function.

OPERATION
At idle, engine speed can be increased by retracting
the IAC motor pintle and allowing more air to
pass through the port, or it can be decreased by
restricting the passage with the pintle and diminishing
the amount of air bypassing the throttle plate.
The IAC is called a stepper motor because it is
moved (rotated) in steps, or increments. Opening the
IAC opens an air passage around the throttle blade
which increases RPM.

The PCM uses the IAC motor to control idle speed
(along with timing) and to reach a desired MAP during
decel (keep engine from stalling).

The IAC motor has 4 wires with 4 circuits. Two of
the wires are for 12 volts and ground to supply electrical
current to the motor windings to operate the
stepper motor in one direction. The other 2 wires are
also for 12 volts and ground to supply electrical current
to operate the stepper motor in the opposite
direction.

To make the IAC go in the opposite direction, the
PCM just reverses polarity on both windings. If only
1 wire is open, the IAC can only be moved 1 step
(increment) in either direction. To keep the IAC
motor in position when no movement is needed, the
PCM will energize both windings at the same time.
This locks the IAC motor in place.

In the IAC motor system, the PCM will count
every step that the motor is moved. This allows the
PCM to determine the motor pintle position. If the
memory is cleared, the PCM no longer knows the
position of the pintle. So at the first key ON, the
PCM drives the IAC motor closed, regardless of
where it was before. This zeros the counter. From
this point the PCM will back out the IAC motor and
keep track of its position again.
When engine rpm is above idle speed, the IAC is
used for the following:

> Off-idle dashpot (throttle blade will close quickly
but idle speed will not stop quickly)

> Deceleration air flow control

> A/C compressor load control (also opens the passage
slightly before the compressor is engaged so
that the engine rpm does not dip down when the
compressor engages)

> Power steering load control

The PCM can control polarity of the circuit to control
direction of the stepper motor.

IAC Stepper Motor Program: The PCM is also
equipped with a memory program that records the
number of steps the IAC stepper motor most recently
advanced to during a certain set of parameters. For
example: The PCM was attempting to maintain a
1000 rpm target during a cold start-up cycle. The last
recorded number of steps for that may have been
125. That value would be recorded in the memory
cell so that the next time the PCM recognizes the
identical conditions, the PCM recalls that 125 steps
were required to maintain the target. This program
allows for greater customer satisfaction due to
greater control of engine idle.

Another function of the memory program, which
occurs when the power steering switch (if equipped),
or the A/C request circuit, requires that the IAC stepper
motor control engine rpm, is the recording of the
last targeted steps into the memory cell. The PCM
can anticipate A/C compressor loads. This is accomplished
by delaying compressor operation for approximately
0.5 seconds until the PCM moves the IAC
stepper motor to the recorded steps that were loaded
into the memory cell. Using this program helps eliminate
idle-quality changes as loads change. Finally,
the PCM incorporates a No-Loadengine speed limiter
of approximately 1800 - 2000 rpm, when it recognizes
that the TPS is indicating an idle signal and
IAC motor cannot maintain engine idle.

A (factory adjusted) set screw is used to mechanically
limit the position of the throttle body throttle
plate. Never attempt to adjust the engine idle
speed using this screw. All idle speed functions are
controlled by the IAC motor through the PCM.


The MAP component may be important since you have a turbo. (Or not)

I asked if Banks did the reflash because they might have some idea why this is happening. Since you are leaning toward the PCM being the cause (& may well be correct) finding if the reflash is part of this issue might come into play & hopefully whoever did it is still around. And if you do replace the PCM I assume you will want a reflash done to it.


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Old 08-01-2019, 12:47 PM
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Rubi -



Thank you for your input. Yes - the OBD-Codes info provides a competent path to testing the IAC circuity, indeed. Going through those levels of troubleshooting unfortunately leaves me in the dark as well, as the engine light resets itself sometimes, and sometimes not. Altogether, very ambiguous.


Additionally, the IAC valve motor occasionally starts buzzing with the ignition on (motor not running), as if it's trying to force the pintle forward farther than possible.



Regarding the reflash...


Banks supplies (via email) a tuning file to flash the PCM via a handheld unit capable of communicating with the PCM. This unit is made by SCT (SCTFlash.com). The tune is developed by Banks on their testbed Jeeps, with the disclaimer that the tune will indeed work for similar setups. This is quite beneficial; I've yet to find a local shop who is equipped to tune the Wrangler PCM. And, so far, so good...after 4 years with this setup I've never had this problem.


As for the MAP sensor...


A portion of the installation process of the setup does involve rewiring the MAP wiring harness, because the stock MAP sensor isn't designed to measure anything but manifold vacuum. The rewired setup allows for the sensor to measure both vacuum and positive pressure.


This does raise eyebrows in terms of dependability...but - according to my scan tools - all the inputs to the PCM from the MAP sensor are registering just fine. I have contacted Banks and asked for baseline values for MAP sensor readings, though. This I still feel the need to confirm.


Now, something weird to note. Just the other day, upon starting the vehicle, the instrument cluster did not react at all for ~5 seconds. The gauges then all turned on and appeared to function normally. This symptom now occurs every time I start the vehicle - no reaction from the instrument cluster for about 5 seconds. Ugh.


Another oddity - my incoming air temp (IAT) sensor resistance measures completely open across its two terminals. Additionally, neither of the two terminals are grounded, i.e. there's no path to ground from either of the two terminals when unplugged. However, when energized with the ignition on and/or motor running, the temperature is registering just fine according to my scan tools.



This seems to suggest a problem with the vehicle's sensing of temperature. Occasionally, the fuel system bumps into open loop due to insufficient engine temperature, despite being at full operating temp...odd.


My tasks in the next couple days are to verify the operation of the CPS, and to reset the PCM using the ignition/headlights trick I've read about.


I shall update as it goes along. Thank you again for your input!
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Old 08-01-2019, 07:41 PM   #4
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OK, good info.

The buzzing may well be telling us the problem (or not).

The P-0505 code indicates the PCM is seeing something (non specific) it needs/expects from the IAC circuit.

Reading how the 4 wire circuit to the IAC works you see how they reverse polarity to open/close the IAC. When the pintle is not supposed to be moving either way both sets are energized. So with key on & engine not running there should be no movement (2 hot, 2 grounded wires. If it is buzzing that suggests one of the circuits is not functioning properly (one wire open), possibly the ground side. If the same thing happens when driving that could cause the pintle to go closed & the open circuit does not allow for opening (no reversing). As long as you are driving you would not notice that until you drop to idle or let off the throttle & (you do note) increased engine braking. On the other hand, if with polarity reversing the pintle could go the other way & go fully open (no reversing) which I assume from the “no load” speed limiter noted in the FSM a fully open state will give an idle speed of about 2000 RPM (throttle closed). Again, probably not noticeable until idling. Being intermittent you never know when the reversing will fail so you could get no idle one time & full idle speed another.

When it is buzzing you might try unplugging the IAC & seeing what readings you get on each of the 4 wires (power/ground??). If you have 2 hot, 1 ground or 2 ground, 1 hot that will tell you a lot.

As for the IAT sensor, remember that is air temp in the intake manifold, not related to the coolant temp. So you could be getting incorrect IAT readings (maybe causing open loop) even with engine up to full operating temp. Possibly related to this is the apparent open ground at the IAT. The sensor is grounded through the sensor ground circuit in the PCM. That should be the black/light blue wire. That wire serves various sensors by having them all splice together at a couple of places, & of note, the sensors include the MAP.

Since this IAC issue is intermittent & may be affected by the MAP I would say you may have a bad splice in the sensor ground. The common splice appears to be S-127, located near the IAC according to the FSM. If that is enough to cause the erratic IAC & code, I don’t know. It would be worth checking into.


Since you have the file from Banks have you tried reflashing the PCM?
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Old 08-04-2019, 09:27 AM
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Rubi -


The observation of the buzzing sounds being related to IAC function is a fantastic observation...thank you! It absolutely follows that the IAC valve is being forced to perform in a different manner than prescribed, causing a buzzing reaction (in this case).


What I've done is re-verify every sensor on the intake through my scan tools, along with the crank position sensor, speed sensor...pretty much every sensor that I can reach and read live info from. Everything appears to be functioning as advertised.


The IAC harness is registering a steady 12vdc on pins 1 & 3, and grounds on 2 & 4; this follows the FSM description of operation (though I don't know which pins are "supposed" to have 12vdc, as the wiring diagram I have in my .PDF FSM doesn't provided any voltage info, only circuit schematics.)



Yesterday I began unwrapping the harness, moving back/away from the IAC motor and towards the IAT sensor and up towards the PCM. Pretty crispy, after 235k miles...


I did not find any evidence of chafed wires or shorts yet.


Using a skilled technique I picked up while working on H-60 helicopters in the Navy, I let the engine run and shook and twisted and teased on the harness in as many places I could reach, trying to affect some sort of change in engine attitude. No joy here either.


For that matter, yesterday - after unwrapping the harness - everything seemed to be operating perfectly while idling: steady vacuum and engine speed at idle; corresponding kick-up and increase in vacuum with A/C engaged; no buzzing from the IAC.



So...today, on a cold start, I'll cross my fingers. Maybe teasing the harness affected some chafed wire in the middle of the harness bundle. Regardless, it's not "fixed" until I know the reason why, and I'll continue along the harness this week until I can verify clean wiring all the way up and down.


Thank you again for your insight - you're a heck of a troubleshooter .
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Old 08-04-2019, 02:52 PM   #6
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It is good that you have 2 hot & 2 ground wires. Of course do you have all 4 when it is dying or high idling? That is the important question, I guess.

As for the possible IAT or MAP grounding issue, having the harness unwrapped should make finding the splice for the sensor grounds easy. Find the one for the IAT & MAP and give it a close inspection.

I think the splice points are soldered in & have been know to fail either from corrosion or even a poor (cracked/broken) solder joint.

Wiggling the wires is a very good test for intermittent electrical problems so use that on the splice too.

If this is a bad ground issue remember that the further up the circuit from the IAT or MAP you get, the more sensors will be affected from a break in the wire so if only the IAT &/or MAP is causing the problem (not verified but possible at this point) the break would be between the sensor’s connector & the first splice point which should be S-127.

The 4 IAC wires go directly from IAC motor to PCM so no connectors or splices. With that said you should unplug the C-1 PCM connector & check the condition of the pins for any moisture, corrosion or pin displacement just to be sure all are making good PCM contact.

Just a thought which may not tell us anything but if this condition returns & as you are coming to a stop & it acts as if it will die, try turning the a/c on to see if it steps up the IAC & then does or does not die. That might indicate a PCM or other sensor (maybe MAP) issue depending on what happens.

Something else not likely related but is the IAT still in the intake manifold or has it been relocated?
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Old 08-15-2019, 05:09 PM
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May have found the culprit...

Rubi -


Took a week off to address all the other aging machinery in my repertoire.


The Jeep was mysteriously behaving until the other day when - low and behold - 3 engine codes popped all at once while driving across the absolutely wonderful roads of Back Bay Boston (not wonderful, to clarify...awful roads...the worst...)


The three codes were the IAT, IAC, and TPS. Clearly, this is actually a GOOD thing.


I've been slow on unwrapping the entire harness, as it's just a cumbersome task; additionally, because the intercooler coolant tank sits on top of the valve cover, it all has to come off to really get in there, and I'd like to combine the task with some other top-end maintenance.


Regardless, with a mirror and a a flashlight in my mouth, I reached in and found the primary driver's side bundle chafing against a large unprotected bolt sticking up at the rear of the head. I believe it may be one of the rear exposed head bolts. You had mentioned this before; I simply missed it.


Though it's tough to see, there is clear visibility of exposed copper strands in a wire that's obviously making contact with something. I'll put some pictures below for reference.


To test out this next theory, I'll be capping the bolt head off to insulate it, and see if the Jeep's attitude changes before going in for the full wire repair task. I'll report back...
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Old 08-15-2019, 07:32 PM   #8
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It sounds like pretty good progress. Good idea to insulate that bolt but remember that if there is more than one bare wire you could still get wires crossing causing any number of unexpected & unpredictable results. Still, it’s a good find.


I know its tight quarters back there but try to separate the wires as best you can especially any bare ones.



There is also a bolt sticking through the firewall behind the head (area) that is known to damage the harness passing near it & really hard to see. As with what you have it can cause unpredictable problems with so many wires in the harness & any one or more may be the one(s) that get damaged. No fun!!



What were the exact codes you were getting?
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Old 08-19-2019, 09:31 AM
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Rubi -


Sorry for my slow replies...life is getting in the way.


Like a jerk I didn't write the codes down numerically. But I do recall them being the P0505 for the IAC valve, P0123(?) for the TPS, and one for the IAT sensor, perhaps P0101...I'd have to look it up.


Since capping the top of the suspect bolt and insulating the ground point, the Jeep has been running fine. Therefore I'm rather convinced the problem exists in that particular spot in the bundle.


I definitely DO have to get back there and separate the bundle and check for other wire damage. I'd be surprised if only that single wire was affected. I'll get around to it and report!


And again, thank you for your continued support in this gremlin hunt. It'll be filed away under "fun troubleshooting moments" once it's all sorted out!
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Old 08-19-2019, 11:16 AM   #10
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In addition to the great advice from Rubi, have you cleaned the IAC plunger & its orifice in the TB with carb or TB cleaner yet? And exactly what brand and model # spark plugs are installed? The wrong single-tipped platinum (platinum on just one side of the gap) plugs are well known to cause misfires and rough idles in newer 4.0 engines with the coil rail ignition system like your TJ has. A couple high quality commonly recommended spark plugs that WILL cause misfires/rough idles in engines like yours include the Autolite AP985 and Champion 3034. Some spark plug guide books erroneously indicate them and similar single tipped platinum plugs as correct but they are not. Three known good spark plugs that are good choices for your waste spark style ignition system include the Autolite iridium XP985, or double tipped platinum (platinum on both sides of the gap) Autolite APP985 or Champion 7412.
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Old 08-19-2019, 12:37 PM   #11
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Don’t worry about the response time.

The only reason for the actual code is there are often more than one code relating to a particular sensor like voltage high or voltage low or intermittent readings. The P-0123 is high voltage which often indicates an open or high resistance to ground which makes sense since it seems you have been dealing with possible sensor grounding issues besides the IAC (P0505 which we know about).

Now that you have found the exposed wiring & hopefully that is the cause it doesn’t really matter unless one or more return. Then get the actual code.


A quick hijack.


Jerry, unless I mistyped it I have filed from a previous posting you recommending the Autolite APP985 (same as here) or Champion 7034, not 7412. Any difference? I have not had to replace yet & would probably go with Autolite but would like the option of Champion too. Please advise.
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Old 08-19-2019, 08:49 PM
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Jerry -


When my idle problems first surfaced a while back, I did my research and immediately took your advice from (numerous) previous posts. The TB came off, along with the IAC valve; both were squeaky clean, exhibiting not so much as a speck of deposit on either the IAC valve plunger or the plunger seat in the orifice.


Moving forward, I smoked the intake manifold, and found a concerning amount of smoke passing through the throttle plate shaft bearings. (After 233k miles, I wasn't too surprised.) This (clearly) gave me reason-enough to upgrade to the larger BBK TB. Better throttle response, yes...but my idle problems still persisted.


I experimented with 3 different size O-rings to seat the IAC valve, thinking that perhaps a gross leak existed between the IAC flange and the TB; no joy. Along with a couple spare IAC valves exhibiting the same idle behavior, I've all but ruled out the TB/IAC valve as being the failing culprits at this point.


As for plugs, I'm currently running a single-point platinum Bosch plug. They are indeed due for a change upon my annual tune-up; I'll take your advice and try the Autolites or Champions.


Though, to note, I've yet to sense any misfires or have any misfire codes. I'm honestly judging the "sensing" of misfires based on the balance of the engine. Even while misbehaving - with the idle speed drooping down to 250 RPM - the idle is smooth and consistent, with no obvious misbalance of firing among cylinders. Furthermore, gently laying into the throttle to force the engine back up to ~800 RPM produces a clean, balanced and linear change in engine speed. Nothing but smooth as the RPMs go up, either.



Rubi -


I should have written down the codes...I know better than to rely on my memory at this point. They had cleared upon restart an hour later.



What I do recall is that they were the IAC valve, TPS and IAT sensor (all related to the top of the intake manifold and common to the same harness); they were all "sensor input high" or something similar; and they all popped simultaneously when driving at a decent clip over a nasty patch of potholes in a construction zone.



I'm anxious to get into the harness and see what other wires have been chewed through. Who knows...maybe I'll fix something that gets me back to 16 MPG again At the moment though, she's still behaving just fine with the exposed bolt covered with a thick rubber cap.


As a quick aside...


Prior to installing the turbo, I simply chased down stations with the cheapest gas...makes perfect sense on an ~8:1 six-cylinder.


When installing the turbo setup at 165k miles (12 years of driving), I yanked the intake manifold. I had to soak and scrape away a solid 5mm of gunk from alongside the interior walls of every passageway. Terrible.



Now, because of the fear of pre-detonation from the forced air, I only run the good stuff (Shell's V-Power, preferably). Currently, 4 years/70k miles later, the intake manifold shines like a diamond under an inspection light. There isn't so much as a smear of buildup on the interior walls.


I'll never debate the use of high-test fuel for power in such an engine as this; however, I'm now rather convinced that the quality of certain fuels definitely makes a difference in an engine's intake arteries...


FWIW.
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Old 08-20-2019, 12:31 AM   #13
Knows a couple things...

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Quote:
Originally Posted by RUBI 4 MY MRS View Post
.. Jerry, unless I mistyped it I have filed from a previous posting you recommending the Autolite APP985 (same as here) or Champion 7034, not 7412. Any difference? I have not had to replace yet & would probably go with Autolite but would like the option of Champion too. Please advise.
Autolite replaced the 7034 with the 7412.
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Old 08-20-2019, 11:08 AM   #14
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Thanks, Jerry.

Now back to regular programming…

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