Still Idling low after IAC adjustment
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Joined: Apr 2008
Posts: 2,342
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From: Dumfries, VA
Car: 1985 Z28
Engine: 334 Stroker Superram 222/230
Transmission: Full Manual 700R4 / 3k Street Edge
Axle/Gears: 3.90 Eaton, Moser, Richmond & More
Still Idling low after IAC adjustment
So I did the IAC adjustment written by vader and followed it EXACTLY as written.
Paperclip and ECM in diagnostic mode > Wait 30 secs and unplug IAC; turn off ignition and remove paperclip > Unplug timing bypass connector and start engine.
At first, the engine died right out as soon as I let my foot off the gas. No problem, let's open that screw up some. So I adjusted it to 500RPM with the transmission in DRIVE (This may or may not make a difference but I do have a 3000RPM converter), then plugged the bypass connector and IAC back in and started the engine.
Now, this is what it does (On a warm motor). When you first fire the car up it will go to 1000RPM as it should for a few seconds, then it will drop down to about 650RPM; exactly where it should be. It will idle like this fine for a minute or two, but then it kicks down again to 500RPM and seems to favor that for idle speed.
This IAC is brand new. I purchased it as a NOS replacement from TPI parts. All the passages in the throttlebody have been cleaned. WTF is going on!?
Paperclip and ECM in diagnostic mode > Wait 30 secs and unplug IAC; turn off ignition and remove paperclip > Unplug timing bypass connector and start engine.
At first, the engine died right out as soon as I let my foot off the gas. No problem, let's open that screw up some. So I adjusted it to 500RPM with the transmission in DRIVE (This may or may not make a difference but I do have a 3000RPM converter), then plugged the bypass connector and IAC back in and started the engine.
Now, this is what it does (On a warm motor). When you first fire the car up it will go to 1000RPM as it should for a few seconds, then it will drop down to about 650RPM; exactly where it should be. It will idle like this fine for a minute or two, but then it kicks down again to 500RPM and seems to favor that for idle speed.
This IAC is brand new. I purchased it as a NOS replacement from TPI parts. All the passages in the throttlebody have been cleaned. WTF is going on!?
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Joined: Jul 2006
Posts: 306
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From: Las Vegas
Car: 1985 El Camino Choo Choo
Engine: L31 Crate 350 w/ TPI
Transmission: GN 200-4r
Axle/Gears: GN 8.5 3.73
Re: Still Idling low after IAC adjustment
It's been a while, but I remember going through this. IIRC it was an iterative process, involving adjusting the IAC, and then adjusting the TPS. Took several tries to get it to settle down. HTH
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Joined: Sep 1999
Posts: 7,072
Likes: 13
From: Philly, PA
Re: Still Idling low after IAC adjustment
Not sure about 85 but in 86 that was the commanded idle speed. And like 450 in gear (automatic trans car).
If that's what the chip is progammed for that's what it's going to idle down to unless you open the throttle plate adjustment so much it idles higher than that even when the IAC valve is fully closed.
If that's what the chip is progammed for that's what it's going to idle down to unless you open the throttle plate adjustment so much it idles higher than that even when the IAC valve is fully closed.
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