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IAC Check engine light

Sirus789

NAXJA Forum User
Location
Ann Arbor
the other day i noticed my jeep got abnormally louder than usual. (i have it straight piped from the cat back) no big deal right, just blowing the crap in the cat out which it was. however when coming back from some wheeling i was doing about 75 and all of a sudden my check engine light comes on. look at the gauges and nothing is wrong. once i get home i run the code and it comes up for a IAC. put it off, put it off until one day the RPMs are really high and i dont want to drop it into gear. so i go buy a new one and install it. code goes away for a min once cleared and now the jeep wont even hardly idle unless you hold your foot there, and then the check engine light comes back with same code. so i was thinking the tps went out on it to. bought one of those and installed it as well. well it didnt work. so i was poking around at my work (chrysler proving grounds) and people are telling me a few different things. one my PCM needs to flashed. two i need a new PCM. three there is something far more serious, like a chassis short or something. any and all input is welcome,another few things to add to the situation is after this check engine light when my left blinker is on it always turns the right one on so i have hazards on in the back. another item is my cruise control wont work. i replaced a clock spring and checked all voltages, vacuum, and even the button. im out of ideas. once again any and all help appreciated.
 
I seroiusly doubt it's a PCM issue. What year XJ?

I think you have several issues, the signal lights are on a completely different circuit from the rest. Let's go for the worst problem first...

Did you clean the IAC portion of the throttle body out? There are some small passages in there and they often get gunked up with carbon, soot, and oil residue. I would grab a can of throttle body cleaner and a bunch of qtips and pull the IAC off the throttle body, clean it all out till the passages are open and you can see metal (doesn't have to be something you could eat off of, but all the heavy residue needs to be gone), then clean the IAC pintle/snout off and reinstall it. I would also disconnect the battery while doing this so that the ECU's adaptive memory will reset and it will re-learn from the beginning, there is a good chance it is getting confused trying to compensate for the new IAC and gunked up throttle body passages.
 
I seroiusly doubt it's a PCM issue. What year XJ?

I think you have several issues, the signal lights are on a completely different circuit from the rest. Let's go for the worst problem first...

Did you clean the IAC portion of the throttle body out? There are some small passages in there and they often get gunked up with carbon, soot, and oil residue. I would grab a can of throttle body cleaner and a bunch of qtips and pull the IAC off the throttle body, clean it all out till the passages are open and you can see metal (doesn't have to be something you could eat off of, but all the heavy residue needs to be gone), then clean the IAC pintle/snout off and reinstall it. I would also disconnect the battery while doing this so that the ECU's adaptive memory will reset and it will re-learn from the beginning, there is a good chance it is getting confused trying to compensate for the new IAC and gunked up throttle body passages.

^This
 
Amen, Kenny. In addition, the symptoms DO sound as though the TPS could also be acting up. I've been through a half-dozen with my '96, and the best one was a junkyard item. I had a brand-new one which acted worse than the original one that started all the trouble. They're compatible from '91 through '96, if yours falls into this range. Best part is, I can buy six or seven from the yard for the cost of one new one. Give it a try.
 
I forget what the exact split year is on TPSes but it's either 95 or 96. Round pin vs flat pin in the connector, otherwise the same... thanks Chrysler!
 
Late '96-think Classic- has the '97+ wiring harness. I use Rock Auto's online catalog to cross reference parts compatibility. Occasionally I'll buy something, too!
 
I always look at the connector on the jeep before even thinking about ordering, then buy the one that matches. Been burned by parts catalogs with wrong year splits too many times not to.
 
I've had a few Fords in my day, and, especially with the Pintos (please don't laugh), you had to know which month your car was manufactured! Seems like they were evolving even as they were on the assembly line...
 
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