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Old 11-10-2016, 01:22 PM
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Idle Air Controller symptoms?

So I've been trying to track down an issue I've had with my 05 TJ for a while now. However, it's recently gotten a lot worse after i swapped my remanufactured engine in.

while in gear, immediately after reving the engine(To take off from a stop) and letting off the gas, the jeep wants to rev itself in pulses. This happened most of the time prior to the engine swap when i was in reverse, and under a load(Backing up the trailer is the best example).

But now after the engine swap it happens quite a lot, pretty much anytime the engine is warmed up and i idle in reverse.

After a bit of research the first thing i assume is the IAC, as it's the only thing(?) that has control over the RPMs in idle. However my symptoms seem a lot different than most IAC cases. Most include high RPMs in the 1.5 and 2ks while in park. When mine only occurs while in gear.

I cleaned that portion of the throttle body and the IAC itself, although i don't think it did much. Maybe made it a little better, but it's too close to tell. I'd like to know for sure before i drop 70 bucks on a part that i'm not even sure if it's bad. That's why i'd like some conformation here before i pull the trigger.

I also have an intake/vaccum leak sound that's audible from the cab i'm trying to track down. It flares up at constant crusing RPMs. Perhaps that could have something to do with it?

Thanks!

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Old 11-10-2016, 02:34 PM   #2
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Fix the vacuum leak asap, not only is it more than likely you problem, but your iac can't work as it should with a vac leak.
Did you pull and clean your iac? If not, it's not clean. Spraying down the intake won't do much. Somtimes you have to remove and literally dig gunk out.

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Old 11-10-2016, 02:48 PM
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Fix the vacuum leak asap, not only is it more than likely you problem, but your iac can't work as it should with a vac leak.
Did you pull and clean your iac? If not, it's not clean. Spraying down the intake won't do much. Somtimes you have to remove and literally dig gunk out.
Yeah i removed and cleaned it. It's different from my 2000 TJ's IAC. That one is more like a probe while the one in my 2005 has a more plunger-look. I did get a pick and scrape off all the gunk i could from the housing it mounts in, and the sensor itself(careful not to damage any sensitive-looking parts).

I guess i'll work on tracking down that vacuum leak. Spraying down intake and vacuum lines with carb cleaner waiting for a change in RPMs is the best way, correct?
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Old 11-10-2016, 02:58 PM   #4
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Mechanics stethoscope is best, carb cleaner will work, but be very careful! An iffy plug wire or hot exhaust could light it up. And after you find and fix the leak, it might still run wonky for a bit till the computer re-adjusts to the proper air fuel ratio.
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Old 11-10-2016, 07:40 PM
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Mechanics stethoscope is best, carb cleaner will work, but be very careful! An iffy plug wire or hot exhaust could light it up. And after you find and fix the leak, it might still run wonky for a bit till the computer re-adjusts to the proper air fuel ratio.
Alright, thanks! I have a mechanic's stethoscope as well so i'll poke around with that along with using the carb cleaner.

Side note, i completely missed that i put this in gen. discussion instead of tech. If a mod feels the need to move it please do!
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Old 11-10-2016, 07:50 PM   #6
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Jeeps is jeeps ha ha,
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Old 11-13-2016, 09:45 AM
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I poked around the engine and sprayed carb cleaner on everything that draws vacuum; absolutely no fluctuation in RPMs. I did, however, remove and re-direct my windstar air box out from the firewall, and down towards the alternator. BAM, vacuum/intake hissing sound gone.
My aftermarket intake always did make a hiss, but it was only during heavy engine loads and on cold startups. Perhaps the 1" MML i installed changed the angle it enters the firewall enough that it hisses more often now? It's happening less often now that I've hooked it back up properly so probably some more fiddling with it's angling will silence it for good.

With that ruled out, i went to back into the driveway this morning. Hit the gas and let off, jeep stalls. So i think I've narrowed my issue down to either the TPS or IAC. Right now i'm leaning towards the TPS, as my issue mostly responds to sudden, sharp changes in throttle position. I'll probably do a little more research before ordering a new $50 part, but i believe that's my best lead right now.
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Old 11-13-2016, 05:10 PM   #8
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...it might still run wonky for a bit till the computer re-adjusts to the proper air fuel ratio.
Several nanoseconds, at least.
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Old 11-14-2016, 05:54 PM   #9
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I'll probably do a little more research before ordering a new $50 part, but i believe that's my best lead right now.
Take it (Jeep) to your local parts house and bring the tools with you to change 1) TPS and 2) Idle Air Control Valve (about 2" further in and parallel with the TPS on the throttle body/IAC). On mine, they are both T20 stars. Also bring some mechanics gloves...hot engine. Both of the sensor plugs (1 each) are simple press in and pull types. My IAC valve was a bit of a pain, so pressing in with a flat tip screwdriver helped on that one. YMMV.

Buy one, go out and install it (3 to 5 minutes of work) and test drive. Doesn't work, take it back off, put the old back on, and exchange the part for the other. Do the same--if neither fixed the problem after your test drive, put the old on and return / save the $$. Parts houses are okay with this (at least in my neck of the desert).

I just did this last night as I had a high idle after the engine warmed up. TPS was ~$35, so I tried it first. No dice. Exchanged it for a ~$67 IAC valve and I'm luckily good as new (I had already cleaned the IAC/throttle body which was my first step). That way you aren't throwing $ at it and these are common stocked parts at O'Reillys, Advance, etc.
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Old 11-16-2016, 08:18 PM
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Take it (Jeep) to your local parts house and bring the tools with you to change 1) TPS and 2) Idle Air Control Valve (about 2" further in and parallel with the TPS on the throttle body/IAC). On mine, they are both T20 stars. Also bring some mechanics gloves...hot engine. Both of the sensor plugs (1 each) are simple press in and pull types. My IAC valve was a bit of a pain, so pressing in with a flat tip screwdriver helped on that one. YMMV.

Buy one, go out and install it (3 to 5 minutes of work) and test drive. Doesn't work, take it back off, put the old back on, and exchange the part for the other. Do the same--if neither fixed the problem after your test drive, put the old on and return / save the $$. Parts houses are okay with this (at least in my neck of the desert).

I just did this last night as I had a high idle after the engine warmed up. TPS was ~$35, so I tried it first. No dice. Exchanged it for a ~$67 IAC valve and I'm luckily good as new (I had already cleaned the IAC/throttle body which was my first step). That way you aren't throwing $ at it and these are common stocked parts at O'Reillys, Advance, etc.

Alas i wish it was that easy. Honestly most of the parts stores around here won't let you get away with things like that. The ones i go to, at least. Electronic parts are a big no-no on returns, they won't take them back if there's even a clue that they were installed. I guess theoretically i could test them then take them back saying they didn't fit? The almost-new TPS that i had left over from my 2000 TJ's throttle body was almost-identical. Except for little fins in the connection that didn't let me plug in the 2005's harness. I i could pass it off as the wrong part while returning it?

I ordered a mopar TPS that should be here Friday. As i'm experiencing other symptoms partial to that part being bad(poor fuel economy, slightly rough idle, and recently my Jeep has been taking an extra half second to start). I shall report back when it is installed.
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Old 12-06-2017, 02:08 AM
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Bumping this thread up from the dead because i finally solved my problem!

So, the TPS was not the issue despite me not posting back after installing it. After that i tried a new IAC, still no dice. I even put in a couple different cam shaft position sensors and a new crankshaft position sensor.
At this point i realized something that feeds the IAC data is what was causing the issue. Reason being; i can hear when the IAC is open and supplying the intake with air because my cowl intake will hiss on cold startups(When the IAC is working) and at certain load and RPM ranges. And when my jeep did the surging/stalling issue, the IAC would sometimes kick in as if it's trying to save the engine from stalling.

Flash forward to a couple days ago(been dealing with my jeep stalling and surging for over a year now!); i was taking a close look at the throttle body and noticed the MAP sensor(which is original) and wondered why i never through of looking up symptoms of a faulty MAP sensor, despite having replaced every other sensor related to the system. I don't ever recall reading about a faulty MAP sensor while researching my problem. I guess these don't often go bad on the 4.0 maybe?

So i read up on faulty MAP sensors and saw a lot of familiar symptoms: bucking, stalling, bad mileage, etc all normally without triggering the CEL(apparently MAP sensors normally don't trigger a light until they have completely failed).

So i ordered a new MAP sensor and all above symptoms subsided. Not only that, but i gained back about 1 - 1.5 MPG.

It turns out that with a faulty MAP sensor, the ECU delivers the wrong fuel/air ratio and can cause some controllers to behave erratically(the IAC for example).

So i wanted to post back for future searchers! I can finally do finite throttle inputs while off road without my jeep stalling out
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Old 04-25-2018, 06:33 PM   #12
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Hey Hexiled Razz, if your still hanging out on the forum, thanks for posting the fix! Been fighting a low idle misfire for a while now and working through the sensors too. But after reading this, I might jump ahead straight to the MAP sensor. Might save me a few $$$. But anyway, thanks for posting back. Not many do once they find the fix.

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