I have been working on IAC control with my 84 Corvette and I am stumped. After the motor is warmed up no matter what I do the idle will always shoot to 1000 rpm and decay. I also have a issue where on cold start the same thing happens. Start - idle shoots up to 1000 rpm and then it will decay real fast instead of a smooth idle down. What items should I be looking at?

 

Have you looked at the IAC Idle Down Rate table?

 

Yes. The interesting thing is hot or cold it will idle down fast at about the same time period. When cold it will initially start at 1400 rpm and then idle down at the same rate. It is odd... I figure it has to be something stupid.

 

On a warm idle set the throttle blades to give between 5 & 10 IAC steps.

If that doesn't fix it make a data log of a couple of start ups. And email it to me. I'll take a look at what it is doing.

RBob.

 

RBob - Email on the way.

 

isnt the 5 too 10 step, of IAC, a little high for a warm idle, ??? aim for the zero ??

 

No.
Not always, on some codes that seems to work best, but not all.