When I drive the ECM idles the car at 1500-2000 untill I stop or tap slightly on the gas. Sort of like a stuck throttle. I do not have a binding throttle or linkage. I replaced the TPS because it was not giving smooth increase. No change.
I also found the TPS sensor was rubbing on my Accel 58mm throttle body. Filed it down, no change.
Hooked up my scanner and the IAC (stepper motor) is ay 47-50 steps during the high idle, according to the book it should be 25 steps. This I think is causing the high idle. I am not 100% sure though.
What drives the IAC and why or when?
I am not along with this perticular problem, read other peoples comments and you will see. www.thirdgen.org/messgboa...00129.html

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86 Camaro Sport
383 Speed-O-Motive Crate Engine, Trick Flow Heads, 58mm Accel TB, 3.73 Auburn Pro, SLP Cold Air Induction and Headers, Dynomax Cat-back, Serpentine belt setup, Dual IROC Fans.

http://www.sethirdgen.org/octride.htm

 

The IAC is driven by commands from the ECM. The PROM is programmed with a desired idle speed and the ECM sends voltage to the IAC in an attempt to maintain that RPM.

The desired RPM changes depending on the conditions of the engine - cold start, warm start, open vs closed loop, etc.

I use Diacom to record the desired idle speed at various engine conditions and the RPM does vary a lot until the engine goes closed loop.

Guys on the PROM board could give you more detailed info.

Hope this helps.

Jake

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1986 Corvette Coupe, 415 CID, Edelbrock 6073s, ZZ9