idle right - Team Camaro Tech
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post #1 of 4 (permalink) Old Apr 27th, 04, 08:35 AM Thread Starter
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89 RS 2.8 auto. my idle seems to be out of place. ive tried turning it up and down to make it right. it runs very low in the morning until it warms up. do i have to go to the shop or myslef can do it. what rpm should it idle at? note the IAC is fairly new not even a year. is the pintle right? how will i know? it runs fine in normal oppration mostly
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post #2 of 4 (permalink) Old Apr 28th, 04, 01:28 AM
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By reading your two posts here, it reads either the ECM isn't controlling the IAC because the ECM is broken or the wire harness between the ECM & IAC is broken.

Advance Auto used to do diagnostics for free. Might want to take the car to them and have them take a look at it. They might even recommend a repair shop.
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post #3 of 4 (permalink) Old Apr 30th, 04, 03:07 AM Thread Starter
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thanks for the advice. how can i see for myself that the ECM is bad? could i run some test? it seems like it works well. im also starting to suspect a leak somewere. this morning when i started up the car, i warmed it up until the temperture went up. the rpms started going up higer at about 2500rpm. when i put it in drive it goes down and wont do it under normal operation nor will it do it when ive driven for a while. please dont tell me the intake is bad or need to be resealed. i just dont get it.
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post #4 of 4 (permalink) Old Apr 30th, 04, 03:10 PM
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You should check out You will find lots of helpful posts there. There is an diagnostic and adjustment procedure for those, though I'm not familiar with the 89 2.8 specifically. So take this with a grain of salt since your setup may be different. From what I remember, the diagnostic starts like this.

Remove the IAC connector, unscrew the IAC and reconect the wires. Then have your assistant put the ECM into diag mode by shorting the upper right two connectors on the diagnostic port. Turn the ignition on but don't start it. The IAC motor should fully extend and then back up 144 counts (3/16" or so). Once it has done this, turn off the ignition, remove the diag jumper, disconnect the wires, reinstall the IAC motor, but don't reconnect the wires just yet.

Some of those engines required an adjustment on the throttle positon sensor which would affect idle if it was off. With the IAC motor in the preset position from above, start the engine and adjust the idle stop until you have about 700 RPMs. The engine should be warm / hot for this. So let it run a while if the engine is cold. Once the RPMs are set, turn the motor off. Then turn the ignition on, and measure the TPS voltage (center pin) to ground (right pin? but not the chassis). The TPS sensor can be adjusted slightly by loosening the two attaching screws. Adjust it for about 0.7 volts. When you are done, turn off the ignition, reconnect the IAC motor (make sure the diag jumper is removed) and start the motor.

If this doesn't help or work out correclty, you'll have to dig in deeper. Most Hanes or even Chilton service manuals should have some troubleshooting procedures for the IAC circuit. Better yet is to get your hands on a professional service manual like Mitchel's. Your local library may have something.

68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI
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