Anyone experience a failed IAC? - Page 2 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 01-29-2009, 11:12 PM   #11
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I unplugged my MAF and had no change. Any thoughts at this point?
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Old 01-29-2009, 11:29 PM   #12
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Are you getting any other codes? It could be your IAC, or your ECT, or your crankshaft sensor. I would hate to have you start changing sensors until you hit the right one. So check for codes again.
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Old 01-30-2009, 07:42 AM   #13
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I have seen an IAC cause idle issues. Afterall, that is it'* one job. The 121 has me thining though. Off to Google to try DTC P0121

Ok.. after googling, I'm going to say the issue is a bad throttle position sensor or wiring to it. Dan, got your manuals handy? Can you give him the colors of the wiring on the TPS. Let'* have him check the +5 and ground for starters. If a scan tool is available, check throttle position by having key on with engine off and pressing the throttle while watching the tool.

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Old 01-30-2009, 08:03 AM   #14
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I think he said that was the first thing he changed. I'll look that up Bill, but I won't be able to do that until tomorrow.
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Old 01-31-2009, 12:53 PM   #15
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I did put a brand new, AC Delco TPS in with no change. I wish someone I know had a Bonny that I could just try switching the IAC without having to buy one. I could certainly reason that an incorrectly functioning IAC could cause this problem. I took it out and cleaned some gunk off it, but no change. It it is slow to react to RPM changes this could be the problem. If I let my foot off the gas pedal slowly it either will not have the problem, or it will not react as severely.

I might run down to a junk yard and buy one for cheap, and a MAF too. I have changed the MAP and TPS, and secured the MAF assembly that was clearing leaking vacuum.
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Old 01-31-2009, 01:17 PM   #16
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Another possibility is your ECT sensor, easy to change. And your crankshaft position sensor. A bit harder to change.
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Old 01-31-2009, 04:22 PM   #17
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Failed Thermostat; Source of P0128 ECT Below Thermostat Regulating Temperature Do you have any temp. issues too hot or too cold?
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Old 02-01-2009, 04:46 PM   #18
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I am not having any issues at all with temperature, and do not have the PO128 code.

I did pickup a IAC at a junk yard yesterday for $5. The problem seems to not be as severe, but is still there.

Here'* a question for you all: When you let up your foot on the gas abruptly on my car the idle dips below 500rpm or actually dies. But starts right up and idles fine. In fact the idle is mostly just fine. Sympton only occurs when taking the foot of the gas quickly, but not if you do it gingerly.

So it is like I have a vacuum leak when the vacuum is at the highest pressure. What might cause that?

Thx for all of the feedback.
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Old 02-01-2009, 05:12 PM   #19
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Almost sounds like your going really lean.

Opps, I forgot to look up that sensor. Looks like dark blue is the signal wire from the TPS Connect your multimeter there and do what Bill suggested. If the TPS is out of wack it could give strange readings and could cause the injectors to lean out.
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Old 02-05-2009, 12:05 AM   #20
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FIXED IT!

I finally sprung for a new MAF and also picked up a PCV and replaced them. The problem continued for a few miles then presto, no more dipping idle and my check engine light went off!

The MAF was about $42 at Autozone, looked like OEM.

I'm happy. Thx for all of the help!

BF
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