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Old 07-28-2014, 02:17 PM   #1
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Very strange IAC motor problems

About a year ago, I had a Check Engine light on with an IAC code. I removed the throttle body and IAC motor, cleaned the throttle and installed a new IAC from the dealer, no more problems. Recently my CEL would come back on and my engine would turn off while idling after driving. It would start right back up like nothing happened and after a few small trips, the light would go out. Happened once or twice over the course of a few months. Now it's happening way more frequently to where I won't make it down the street, haven't gotten to scanning the codes yet, but I will shortly, but this is the same exact problem that lead me to replace the IAC in the first place. Any suggestions would be great. Thanks

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Old 07-28-2014, 02:40 PM   #2
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Oh, forgot the important stuff, lol...it's a 2006 Jeep Wrangler Rubicon 4.0L Automatic

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Old 07-28-2014, 02:51 PM   #3
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And the code that I have is P0508 Idle control system circuit low.....same as I had a year ago.....thanks in advance

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Old 07-28-2014, 09:29 PM   #4
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I would think possibly a short to ground is the issue. The circuit low code usually shows up with that. Check the wiring at the back of the valve cover. The back head bolt on the left side ( drivers side ) is a stud bolt and I have seen the bolt work it's way through the plastic convolute tube and into the wire harness
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Old 07-29-2014, 10:48 AM   #5
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Alright, I opened the long plastic housing that runs along the back of the valve cover and pulled, what part of the harness I could, out and didn't see any chaffing or damaged wiring. I looked where it's attached to the stud, it had not rubbed thru. Excellent call though, I thought that would've been it.....still looking

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Old 07-30-2014, 09:32 PM   #6
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Well crap.... That's the first place I check when dealing with any high/low codes are present. The PCM supplies the 5 volt sensor supply on the same wire to all the sensors so I would doubt that wire, or PCM supply, is faulty. It would have to be the IAC signal return wire or the PCM itself. With the engine idling, I would start wiggling the wiring harness that leads behind the valve cover and goes over to the PCM. That is were the motor movement would affect the wiring. Also you could try the tap test. With the engine idling, try tapping on the PCM with the handle of a hammer. Don't beat the crap out of it, but a few good knocks may make it stall or stumble. I've seen many problems with a PCM( engine computer ) found that way
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Old 07-31-2014, 12:24 AM   #7
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I apologize, this morning I found it, but haven't had the chance to post because I had to get to work shortly after. But u damn near hit it right on the head Chaos, only it had rubbed thru the split loom on the PASSENGER side of the valve cover stud. Made the repair, which was a pain to get to because it was an inch below where the harness splits off so had like an inch of wire to work with, and secured the harness away from the valve cover. Drove it for an hour after clearing the code, then drive it to work, which was another hour on the highway, and streets, stop & go traffic and massive pot holes (sweet home Chicago, lol) and haven't had any problems. So thanks a million Chaos!! U are a HUGE help

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Old 07-31-2014, 09:04 PM   #8
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Happy to help and at least send you in the right direction
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Old 07-31-2014, 11:54 PM   #9
Knows a couple things...

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Nice call Drivnchaos!
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Old 08-01-2014, 08:38 AM   #10
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Quote:
Originally Posted by RhinoTank View Post
...it had rubbed thru the split loom on the PASSENGER side of the valve cover stud.
I had a similar problem, except it was where the harness rubbed on the top edge of the a/c accumulator. And my problem killed the engine while driving down the highway. All TJ owners would do well to add some armor to those wiring looms running around the rear of the engine compartment.

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