I've been having some idle problems which seems to be a common problem. I've adjusted the IAS and TPS but still get the idle stuck sometimes at 1500 or so but will gradually come down (when the cluth is in). Sometimes it seems to cycle between normal and 1500 - just a couple of times before it evens out. When I start in the morning the IAS=50steps and the TPS=0.58. Later in the day when I start the IAS=9 and the TPS=0.58. What I want to know is this: what factors control the idle? Obviously the TPS has a lot to do with it - at least the adjustment of the TPS. I guess the position of the IAS effects it as well. What else is there? Looking at the TPS and the IAS on my scanner as I'm driving doesn't seem to provide any clues - they both seem to be behaving. What am I missing?

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1988 IROC-Z
5-speed (was 7R4)
Edelbrock TES

 

Have you changed the chip in the car? I see it was an automatic. I believe that everything controlling your car in the warm up transmission, etc. is programmed on the chip. I do believe thatyou will need to have a new one made.

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Hank
87'IROC Z28
Hanks 87 IROC

 

I got a new stock chip for a 5-speed.

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1988 IROC-Z
5-speed (was 7R4)
Edelbrock TES

 

I'd make sure the TB bores are clean and "degunked", you may need to take the TB apart and clean the IAC passages, and the IAC pintle as well.

The IAC counts you mentioned shouldn't give you 1500 rpms (least on my car they won't...when fully warmed up I have like 28 or so counts idling at 750 RPMS...don't recall the faster idle on start up...

 

Thanks Mike. Won't the idle be increased when you first startup and if so, what causes the faster idle? IAS or TPS?

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1988 IROC-Z
5-speed (was 7R4)
Edelbrock TES

 

I believe it's a few things that determine idle speed...

CTS reading first off...this will set a "cold start" injector pulse.

It also sets the IAC (just for clarity it's referred to as the Idle Air Control valve).


I'm not sure if the MAF is used for initial startup refernces or not.

I can look through the manual and see if if there is reference to it.

The TPS should never change it's idle position voltage.