3rd IAC Valve taking a crap? - JeepForum.com
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post #1 of 8 Old 12-13-2011, 07:45 AM Thread Starter
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1997 ZJ 
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3rd IAC Valve taking a crap?

Guys- I have a 5.2L ZJ Limited with 133K miles. original Idle Air Control valve took a poop and I couldn't keep it idling. Replaced- started right up and ran fine. About a week later, rough idle, would literally die in reverse after i back down my driveway, then finally die- would start with some pedal, but not idle and die as soon as i take my foot off. Replaced IAC again, same story, so I'm beginning to think something is causing it to either stay closed or not open?? I'm stuck.

Took hose off PCV valve, so it's running fine for now, but I'd really like to get to the bottom of this failure. Anyone have an issue like this or can point me in the right direction, please? Much thanks.

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post #2 of 8 Old 12-13-2011, 12:10 PM
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Try cleaning your throttle body, i did and it changed my Jeep completely. Use some sea foam if you see it is really dirty...also of that doesn't do the trick check your throttle position sensor...it's the one on the throttle body on the side, drivers side.
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post #3 of 8 Old 12-13-2011, 12:18 PM
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1996 ZJ 
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maybe your running rich causing it to carbon up quicker? or maybe the throttle body needs cleaned. try some seafoam and maybe a new tps. also op the map sensor is right next to the tps on the same side

'96 ZJ Orvis 5.2L (Mossy Oak Edit.)- UC+2" BB, Thrush Turbo, 2 12s, Lots Of Stickers
You drive a tj, we drive a zj. We have more power while you get more shower. We get the v8 while you get there too late. You have 2 doors well, we have 2 more. Ours costs a grand while yours has a price we cant stand.
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post #4 of 8 Old 12-27-2011, 10:48 AM Thread Starter
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So, had a buddy with a performance shop take a look at the IAC. Was able to test it on his bench and it was fine. Also put a meter on the harness (ECU side & IAC side)- no short. I replaced the ECU with a reprogrammed unit from one of the recommended vendors from another post- started right up, but now I'm having some of the same symptoms again. Almost dies in reverse right before I shift into drive, dash lights flicker wierdly sometimes, rough idle & stalling. In a few days, it will either turn over & not start or will die while idling. If I remove the PCV hose and create a vaccum leak, she will start right up (if I remove the IAC, it will be in the closed position- fully extended- and seems to be what is causing my Jeep to turn over but not start.

What am I missing? Is there any other part of the air/ gas system that would cause the IAC to malfunction? I was thinking about leaving the PCV hose disconnected and just fashioning a filter to fit in there just to keep the air clean coming in.
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post #5 of 8 Old 12-27-2011, 11:19 AM
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If you reset the computer is it ok for awhile?

If and when its running ok try tapping on the IAC with a screwdriver and see if you get a stumble or a stall.

Guessing but I would think the TPS is involved.
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post #6 of 8 Old 12-27-2011, 12:36 PM Thread Starter
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I know the IAC is working correctly. Well, unless it is not getting a proper signal, but that would come from the computer, so what could be telling the computer to close that valve? How does the TPS play into this mix? I took that sensor out and didn't really know what it was supposed to look like but it was clean as a whistle, so I put it right back in the way it was.

I'm a little stumped, but have a workaround at least...
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post #7 of 8 Old 12-27-2011, 07:04 PM
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I'm guessing the computer has to learn zero throttle from the TPS.
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post #8 of 8 Old 12-28-2011, 12:44 AM
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1994 ZJ 
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I had replaced my PCM in order to solve mysterious sensor issues. I would reset PCM, and all was well for a short time. I would start her up, sometimes CEL would come on on cold start, then Idle rough. I would turn off and restart, and no CEL.

I added a small amount of carbon conductive grease to the PCM pins with a q-tip, and the problem went away...I chased lots of false codes, IAC, MAP, TPS, NO O2 signal, trans was flashing Temp sensor, and output speed sensor. ALL went away after greasing the pins. 300 miles later, no issues..
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iac , idle , stall

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