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Old 03-29-2011, 07:55 PM   #1
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High idle and DTC driving me nuts!

Been having a high (800-1000 depending on its mood) and bumpy idle for a month or two+ now. Here is what I've tried
  • Cleaned TB and all sensors, especially IAC
  • Replaced TB and all sensors with junkyard replacement
  • Sprayed intake manifold with throttle body cleaner while idling
  • Sprayed and checked vacuum hoses and elbows to best extent
  • Checked *most* of the intake manifold bolts (anyone recommend techniques for the bolts underneath the intake manifold?)

None of those have helped. I am thinking the following may contribute to idle speed but I'd like some forum help on this one
  • Engine coolant temperature sensor
  • O2 sensor
  • CPS

Any help is greatly appreciated. I know the idle isn't that high but it's driving me nuts along with the DTC

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Old 03-29-2011, 11:52 PM   #2
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And of course you did disconnect the battery for 8 hours or more - that resets the computer to learn the new sensors.

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Old 03-29-2011, 11:56 PM   #3
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Did you check your vacuum lines for cracks and leaks?
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Old 03-30-2011, 10:46 AM   #4
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Yes I did 8+ reset many times and again before using new TB and sensors

I checked the vacuum lines to the best of my ability as said in the OP. There's a lot of them so I may try again.

It seems sensor or pcm related because it's so sporadic, it isn't constantly high like a vacuum leak would be?
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Old 03-30-2011, 11:41 AM   #5
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When does it start running bad? Immediately after starting? About 1 or 2 minutes after starting? Or only when fully warmed up?

How 'bout after a warm restart?

Only after driving driving it hard, then down to an idle?

How does it run at cruise? Under load? Mid range? Surging? Bucking? Backfiring?

Odors from the exhaust? Cruise, idle etc?

How 'bout when it's idling high and you quickly "tap" the accelerator - drop down then?

Those are all potential clues, the more you can tell us the better.

A small exhaust leak "upstream" of the upstream O2 sensor can upset the idle speed, but only after the computer system is fully "on line" - fully warmed up.

When totally cold the PCM runs on preset inputs, the O2's don't have any influence.
After a minute or so the PCM does use them as inputs, but they still aren't very influential. Once it's fully warmed up - 2 to 5 minutes, the PCM depends on the O2 sensors.
That's why the cold vs warm info is so important.

The big connector on the PCM, make sure the connections are clean. Remove any corrosion with a good electrical cleaner. Not WD or oils.

When you sprayed looking for a vacuum leak, what chemical did you use? Most carb cleaners are fairly useless for finding a vacuum leak unless it's a giant hole. This sounds more like a small intermittent leak.

Heater working properly?
If it was here, the first thing I'd grab is my propane - but we are on opposite sides of the country! Do a search on here for "propane trick". I think I've posted it here, I wrote it years ago in my book, but it still applies. It's a simple tool you can make for about $10-20, but super super handy.
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Old 03-30-2011, 03:12 PM   #6
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Quote:
Originally Posted by rrich View Post
When does it start running bad? Immediately after starting? About 1 or 2 minutes after starting? Or only when fully warmed up?
Basically after starting. I understand until the engine is in in/near closed loop it wants to idle high around 1000rpms but even when I put it in gear it has a tendancy to "pull" much more than idling in gear than normal. I'll double check this one though because it might be the make or break between sensor vs leak

How 'bout after a warm restart?
Still happens

Only after driving driving it hard, then down to an idle?
Any driving conditions, sometimes at a stop it'll float above 1000 or it'll bounce around 800 up and down

How does it run at cruise? Under load? Mid range? Surging? Bucking? Backfiring?
It runs completely fine except for this stupid idling issue. However last summer I did get some hesitation here and there which I was trying to troubleshoot by replacing the TPS

Odors from the exhaust? Cruise, idle etc?
No odors from exhaust, crappy mileage as of late, usually 16-18 but I've been down to 14-16 at best, could be winter blends though

How 'bout when it's idling high and you quickly "tap" the accelerator - drop down then?
When it's acting up and I blip the throttle it'll usually sink down to almost normal speed then bump up and do it's usual dance

Those are all potential clues, the more you can tell us the better.

A small exhaust leak "upstream" of the upstream O2 sensor can upset the idle speed, but only after the computer system is fully "on line" - fully warmed up.
I'd be curious if I have a minor exhaust leak. I think I have the split manifold (2 mini-pre cats) so I think the probability is lower but it is worth checking. I'll need to get out there with a flashlight at night

When totally cold the PCM runs on preset inputs, the O2's don't have any influence.
After a minute or so the PCM does use them as inputs, but they still aren't very influential. Once it's fully warmed up - 2 to 5 minutes, the PCM depends on the O2 sensors.
That's why the cold vs warm info is so important.

The big connector on the PCM, make sure the connections are clean. Remove any corrosion with a good electrical cleaner. Not WD or oils.

When you sprayed looking for a vacuum leak, what chemical did you use? Most carb cleaners are fairly useless for finding a vacuum leak unless it's a giant hole. This sounds more like a small intermittent leak.
Used throttle body/carb cleaner

Heater working properly?
Heat is working properly

If it was here, the first thing I'd grab is my propane - but we are on opposite sides of the country! Do a search on here for "propane trick". I think I've posted it here, I wrote it years ago in my book, but it still applies. It's a simple tool you can make for about $10-20, but super super handy.
I don't have a propane source and I'm not sure if I am too comfortable dealing with it. I feel the mechanical fan always blowing would be a problem with trying to slowly drip it into a leaky area of the intake
See above
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Old 04-02-2011, 12:38 PM   #7
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I poked around with my scanner today. Here is the freeze frame from when the DTC fired. "Normal" idle RPMs should be 650ish right? I'm surprised this code would fire at 768 to be honest



I also grabbed a minute or two of RPM and O2 sensor data. Could anyone help me interpret the O2 sensor data? I feel that they are working fine from what I see here but I'm not 100%

RPMs


O2 Sensors Bank1/2 Sensor 1


O2 Sensors Bank1/2 Sensor 2
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Old 04-02-2011, 02:09 PM   #8
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Not trying to derail but what scanner do you use? Thanks!
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Old 04-03-2011, 08:48 AM   #9
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I have an ELM327 usb to OBD-2 cable which I then hook up to a laptop that has various scanner software. I spent like 20 on the cable, I'd recommend trying to find a cable and software suite that does O2 diagnostics, etc

Does anyone know if the CPS could cause this?
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Old 04-03-2011, 09:18 AM   #10
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What software is it? Thanks!
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Old 04-03-2011, 10:17 AM   #11
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The software is Digimoto V, I paid for it but I'm not sure if I'd recommend it. It seems a lot of the free software out there does what this does, however the GUI on this suite is pretty nice
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Old 04-03-2011, 12:13 PM   #12
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During idle ur jeep is operating on an open loop strategy anyway. My jeep was doing fine and all of a sudden, it starts idling at like 1500 rpms. I previously had a code for an iac, so I cleaned the crap out of it, did a fuel induction service, and all seemed fine. Then out of no where, I go into walmart, come back out and high idle from then on. I bit the bullet and bought an iac and a can of carb cleaner to search for vacuum leaks.
I installed the iac and started it up, still seemed to run a little high. So I get my high tech diagnostic tool out and start hosing down known problem areas. I find a small leak on #6 intake runner and a big leak on #2 injector o-ring. I'll wait until I'm back at the shop Monday to deal with the intake leak, but I did go ahead and fix the o-ring leak. Made a big difference. Just another place to check if u hadn't. Good luck.
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Old 04-03-2011, 04:16 PM   #13
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Didn't think to check the injector o-rings. Did you just hose the area by the injector/head down to check em?

I changed plugs yesterday to OEM coppers and it didn't help
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Old 04-03-2011, 05:08 PM   #14
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Yep. Once saturated, I could hear and see #2 sucking bad.
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Old 04-03-2011, 08:43 PM   #15
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Does anyone know how to home smoke test your intake? My buddy said some places have bottles that put out smoke and it'll seep from any leaks although it isn't pressured
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Old 04-03-2011, 08:51 PM   #16
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ever think about the tps? not sure if that could be it, but if its not sensing right when your at 0%, like the sensor jumps from thinking its 0-5 say, then it could cause the weird idling, I would think.

I have a rough idle also, but lately its been good. I was messing around a little driving full throttle trying to get it to respond correctly, and when driving up my road my rpms were all over the place weird, leading me to think its the tps even more, for me that is.
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Old 04-03-2011, 08:57 PM   #17
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My previous TPS was new and I replaced my entire TB with all 3 sensors (MAP, TPS, IAC) and the problem still occurs. My scanner is reporting a craptastic throttle position range of 11%-75% which I feel is normal for this year since I've gone through several TPS (OEM and aftermarket) that have this range
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Old 04-04-2011, 03:18 PM   #18
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Bumping this uppp
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Old 04-04-2011, 09:30 PM   #19
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I've smoked intakes b4 using a smoke machine. Same thing u use to find evap leaks. The trick is u have to do it when the engine is cold and block off the crankcase breather system. Use a bright light and see where the smoke is coming from. I've also used that to find oil leaks, wind leaks in weather stripping, really ur imagination is the limit. Works great just takes a minute.
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Old 04-05-2011, 07:51 AM   #20
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Have you tried using the smoke in a can from AZ or similar? I don't have access to a smoke machine and I've read shops will charge around 100
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Old 04-06-2011, 12:41 PM   #21
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Never used any "smoke in a can" products b4. With the engine running, u should be able to find a vacuum leak with a can of carb cleaner. Just be accurate and know what ur spraying. It took me 2 different times b4 I found the vacuum leak on #6 manifold gasket bc it was covered in mud and I had to clean that off first. Good luck.
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Old 04-06-2011, 01:10 PM   #22
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I got a vacuum gauge yesterday to help me out too, hopefully this weekend I'll have some time
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Old 04-06-2011, 04:54 PM   #23
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Easy way - Block off the PCV, have a friend that smokes blow smoke in the intake manifold through a hose.

No friend?
Big Turkey baster, some vacuum hose, a Tee, and a cigarette:

Rig the turkey baster into a Tee, one hose goes to the manifold, the other to the cigarette.

Squeeze the bulb, pinch the manifold hose, let go the bulb - smoke draws into the baster.
Pinch the cigarette hose, squeeze the bulb - smoke gets pushed into the manifold hose.

Works for me.

For a simple smoke test with a professional smoke machine in my shop I would have charged about $10.

But it wasn't a service I offered per se - it was all part of troubleshooting a problem. It's like charging more to use an impact wrench, a scope, or more to use any tool.

A professional smoke machine makes smoke from heated vegetable oil.
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Old 04-06-2011, 05:18 PM   #24
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Will cigarette smoke hurt my Jeep, or give it manifold cancer lol

I'll give that a try tho, should I block off the throttle body port also because smoke may leak through the IAC port? Will non pressurized smoke be enough for the longer vacuum lines?
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Old 04-06-2011, 07:26 PM   #25
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The Jeep may feel a little dizzy at first, but it'll eventually like it. It could be habit forming, then eventually cause breathing problems.

If you see it coming out the TB you know what it is. A rag stuffed in the TB will stop it.

Blowing or even the slight pressure of the turkey baster will get the smoke down through things - especially if there's a opening or leak at the other end which will allow it a place to go.

Look closely at the lines to and from the charcoal canister too. Under the manifold, is another place it could be leaking.

If still not found, try plugging the lines from the intake manifold to the canister - if something's awry in the canister, it too could cause idle problems. A sticky purge valve?
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Old 04-06-2011, 08:52 PM   #26
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Very good advice, I'll try this out! The hardest part is finding a cigarette because I don't smoke lol
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Old 04-06-2011, 09:56 PM   #27
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I quit too - right after my first heart attack! 3 packs a day most of my life - unfiltered of course.

Since I don't want to even be tempted - I came up with the turkey baster idea.
I always hated candy cigs - menthol, so that what I use to test it now. The pack I have is about 5 years old - really nasty! But it works.
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Old 04-07-2011, 05:52 PM   #28
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I didn't have time to try the smoke trick today, still looking for a cigarette and a turkey baster. However I did get to try out my vacuum gauge and a couple other things and I have more results.

Measurements were taken at closed loop fully warmed

At idle: 18 in. Hg rock solid
Blipped throttle to WOT results in vacuum drop to 0, then up to 25 and back to 18 very fast

I took these measurements directly at the intake manifold where the brake booster attaches. In hindsight I should try a different location to verify that the brake booster isn't leaking vacuum. However the idle was the same with the brake booster disconnected and plugged with my gauge.

With these results it would appear I in fact do not have an vacuum leak, is that correct or would a minor vacuum leak not be noticeable on a vacuum gauge?

I then turned my focus to my scanner. I noticed that my MAP at idle reports 41kpa, which converts to 12 in. Hg at idle, this seems very low compared to my vacuum gauge, could this be the problem? When blipping the throttle to WOT the MAP jumps to 100kpa and then drops to 15ish and back up to 41kpa.

I busted out the DVM and measured the MAP and TPS voltages. Grounds are solid, 5v reference floats at 5.12V

Key ON engine OFF MAP output is 4.72V
Engine Idle 1.6V
Blip in throttle resulted in an open circuit and then the voltage went down towards 0 and back to 1.6. This open circuit could be that the change was too quick for the DVM or something wrong with the MAP.

TPS: Idle throttle: 0.595V
WOT 3.8V

I'm thinking of taking off the MAP and cleaning inside the hole of the sensor itself. What chemical would be safe for this? I've seen MAP cleaner at Autozone but would rubbing alcohol, electrical cleaner or carb cleaner work too? I've also seen on a different thread that rrich has seen the MAP connector hose collapse under vacuum, I'll check mine out too

I took some short and long term fuel trim measurements from the scanner too. I'll have to analyze them and post back later.
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Old 04-07-2011, 06:14 PM   #29
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I think your MAP sensor doesn't have a hose, it's right on the TB.
Check the wires to it - look and shake them. If I remember right, that MAP harness has a splice about 6" back from the connector - check it.

It looks like the MAP sensor is reporting the wrong info.
It's reading way low and should never read open circuit. It's not your meter - your digital meter "holds" the readings long enough to read, then takes another sample. If its showing open temporarily - believe it.
You should also be able to see it with your scanner - but remember the scanner is "seeing" interpreted voltage from the PCM, not actual MAP sensor readings. The PCM may smooth it out.


I don't thing they are terrible expensive.

A small vacuum leak won't necessarily show on a vacuum gauge.
The smoke will.
Or propane - most carb cleaners don't burn any better than water. Propane burns almost like gasoline. Starting fluid works well too, but the liquid often washes dirt in the leak, temporarily plugging it. And it puddles - a big fire hazard.

Smoke is the most effective and the safest.





Rubbing alcohol may work, but it may also kill it too.
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Old 04-07-2011, 06:19 PM   #30
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I have my old MAP, I'll give that a try but chances are since it was having the same problem before maybe both MAP sensors are bad. Either way I'll try the smoke test this weekend and keep posting results. I do have some interesting STFT and LTFT along with O2 sensor results I will be posting tonight once I figure out how to work excel the way I want it

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