iceman0028

Hi guys,

I am brand new to this site and new to owning a corvette but I am having a problem with my 1985 corvette...problem I bought the car it kinda had a idle problem when the car is ice cold it has a fast idol but whe it reaches operating temp while driving it it gear at a stop light the idol gos up then down and it will do this till i give it gas...
now so far this is what i have done... i removed the thoddle body cleaned it replaced the idol air control motor and the tps and replace the throddle body gasket..
now since i have replaced all this the car will now mantain a idol but now it idols in park at 1200 rpms and i grear its at about 9200 rpms any ides on how to get the idol down where it needs to be????

John A. Marker

First I am going to assume that your 9200 RPM is a typo and it should be 920.

1) Check all hoses to see if you have a vacuum leak.
2) Check the TPS to verify that you have set it to .54 volts with the key on car not running. Check to see that the TPS arm is not bent and rubbing against the throttle body.
3) Do you know how old the injectors are? Possibility that not all of them are firing consistently.
4) Pull off the hose to the fuel pressure regulator and check to see if there is any fuel in the hose. If so, the diaphragm in the FPR is toast and needs to be replaced.

Those are areas to check.

Welcome to the Forum.

aklim

I'd certainly check for leaks with a propane torch WITHOUT THE FLAME ON AND GAS FLOWING

Do you have a scanner? I would check the IAC counts and use them to adjust the idle speed.

iceman0028

Thanks so far guys I will try your sugesting tonight let u know how I make out

aklim

Not really interested in who you make out with or what make up you use.

Muffin

Have you tried to adjust the idle using an FSM?

aklim

Engine will probably break at that speed of 9200 rpm if it is stock and you run it for long.

I just had a thought. How do you know what the RPM is? Do you have a tach on it or what? I am at 300 rpm above what my inductive timing light from Snap On says and that was pretty accurate.

aklim

I'd do the timing check first and then idle and then the TPS, assuming all is well and there are no leaks.

I don't like the FSM method myself. I prefer to set it thru IAC counts. That way, in future, when mods are done and the command idle changes, you already have been setting it via counts and not just FSM. To set it via the IAC counts, you need a scanner. Something you should have if you don't want to fork over money to a shop for every MIL (Mother In Law or Malfunction Indicator Light, your choice).

SQUIRMIN VERMIN 84

All C4's come with tachs. I assume that's what he was looking at.

aklim

True but for whatever reason, my 91 Firebird tach was spot on but the Vette tach has been known to be funky. When checking RPM I use my timing light which has an inductive tach or the scanner which reads what the ECM is seeing. They have always agreed but the tach in the car is always off.