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Old 12-14-2015, 09:23 AM
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Re: HIGH Idle

Originally Posted by Injuneer View Post
"camaroken" has not returned to the site in 6 years, so not likely he will reply.

To me, it sounds like a defective coolant temp sensor. If the ECM thinks the engine is very cold, it raises the idle RPM and richens the A/F mixture.
thanks for your reply i guss i should have went into more detail about my iroc. its a 1987 5,0 tpi all stock, i have changed egr, tps, coolent temp, iac,still same high idel it will spin tire when u drop it in gear, i have engine light on, i can unplug iac and nothing changes, somtimes after i drive the car for a hour or so it does come down a littel but when i shut it off its high again, ps i also changed plenium gasket, thus car is driving me crazy im abiut to switch over to a carb setup? any help please
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Old 12-14-2015, 09:55 AM
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Re: HIGH Idle

Actually, I think you would be better off starting your own thread.... there is a lot of bad info in the posts above.

You indicated the check engine light came on. What is the code?

Have you checked the coolant temp sensor resistance vs. temperature to verify it's accuracy? Have you checked for the correct voltage on the black and yellow wires to the coolant temp sensor (sensor unplugged)?

Have you checked the resistance of the coils in the idle air controller for continuity? Contrary to what is posted above, the IAC does not set a code if it is faulty, and there is no feedback to the ECM indicating whether it is working correctly or not. Unplugging the IAC won't change anything. It is a pintle, controlled by a "stepper" motor. Pulses from the ECM open or close it in steps. If you unplug it, the pintle will not move, just stay where it was last positioned by the ECM.

This is 4th Gen/LT1 stuff, but the principles are similar:

4th Gen LT1 F-body Tech Articles


Finally, have you verified that the throttle stop screw is not extended out too far, holding the blades open to the point where the IAC can no longer control the idle? Have you verified that the cable or the throttle quadrant is not hanging up, leaving the blades open?
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