Anyone experience a failed IAC? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 01-27-2009, 10:50 PM   #1
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Default Anyone experience a failed IAC?

I have been dealing with an idle problem where when I come to a stop, or near stop, take my foot of the gas SOMETIMES the engine dies. I have an error code 121 (TPS) and replaced it. Of course it didn't fix it. Checked for vacuum leaks, seems OK.

Can a faulty IAC cause this?
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Old 01-27-2009, 10:58 PM   #2
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It is a possibility. Could also be a MAF problem. To test that you can unplug the MAF and drive without it. No more the half throttle when doing this. Your engine will run on the VE table instead of the MAF table. You will throw a check engine light when you do this. But if it runs better, it'* a good chance your MAF is the problem.
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Old 01-27-2009, 11:02 PM   #3
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Dan, that'* a good test. My MAF was rattling around when I started looking so at first I thought that was it. I jury-rigged it where I believe it is sealed and tight. I'll try it unplugged and see what happens.

Thx.
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Old 01-27-2009, 11:10 PM   #4
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A bad connection on the MAF will give you a rough idle and stalling when you stop
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Old 01-27-2009, 11:23 PM   #5
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So if I unplug it entirely will the car run OK?

The plug connection is fine, but the tabs that hold it in place a weak (one is cracked). This is what I jury-rigged.
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Old 01-27-2009, 11:45 PM   #6
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Your car will run fine, just don't go past half throttle. I ran 2 days without my MAF when I was doing a volumetric efficiency tune
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Old 01-27-2009, 11:51 PM   #7
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Got it.

Just out of curiousity, what happens if I go over 1/2 throttle?
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Old 01-28-2009, 12:04 AM   #8
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Your engine could go lean, not a good thing. What your doing is running on the VE table instead of the MAF table. So the PCM doesn't know exactly how much air is going in.
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Old 01-28-2009, 01:43 AM   #9
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Same problem I had with a 1990 SSE trying to die at a stop light from what I remember. I had to change MAF. But my code was for the MAF. Symptoms sound very close.
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Old 01-28-2009, 12:36 PM   #10
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I also have the 121 and 108 codes, 108 relating to the manifold pressure, and 121 to the TPS.

After I clear the 12" of snow on our driveway (and 3' at the end of the driveway where the snowplows leave it), I will disconnect the MAF connector and see what I get.
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