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Need help with diagnosing a high idle

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Old 07-01-2015 | 02:34 PM
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An IAC count at 0 should mean the IAC is completely closing off the IAC passage way in the TB. That is if the PCM has the circuits to control it and if it is wired for it. It could mean that it is all correct and the PCM is commanding 0 in an attempt to lower the idle speed. Use the bidirectional controls in the scanner to command a certain IAC count and see if the IAC position follow what you command. If it does, they you are getting air in the engine from a source other than the TB/IAC. The only way an engine can increase rpms is to give it air. Also have you verified that the TB is completely closing?
Old 07-01-2015 | 02:41 PM
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Originally Posted by 1976CamaroGuy
Looking at the IAC table on this spreadsheet it starts at around 203, then goes to 315 at one point, then drops to zero for a bit

Then slowly picks up from 20 or so until around 183 before I shut the car off

Is this normal? Or anything out of wack
Looking at that I'd say you need to find the air leak.
Old 07-01-2015 | 02:48 PM
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To clarify I see your IAC counts starting out at 183 and going to 0. The PCM is trying to lower the idle speed by closing the IAC.
Old 07-01-2015 | 03:37 PM
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Guys, I taped up and blocked the IAC port on the throttle body (removing the IAC valve) and the car started up and purred like a kitten at around 750 - 800 rpm

Put the valve back in and the RPM jumped to 1500 - 1800

It's GOT to be a bad IAC, programming or something in the harness

I'm going to double check my wiring and try and figure out how to test the wiring to make sure I am getting the appropriate signals

Throttle plates are closed BTW when it is idling high
Old 07-01-2015 | 06:47 PM
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Got it fixed, I bought that new IAC and was still having issues so I decided to swap out the stock TB for the aftermarket polished one I bought a few years ago.

Started right up, idling a hair below 1000 rpm and staying there. I swapped this aftermarket for a OEM one a while back when I was troubleshooting but I guess the IAC was bad then, and the used original TB I bought have had issues as well.

All is good now



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