I've got an '87 Trans Am with a 305 TPI and 700R4.
When I first start it, in park it idles at 1200-1500 rpm for a minute or so, then very slowly drops to 500-600 rpm. If, during this time, I touch the throttle at all, it settles back in high, and slowly begins the drop again. Drive the car, and come to a stoplight, and it idles fast, slowly dropping as I sit at the light. Even after an hour of driving, the same story...so it doesn't go away after operating temperature is reached.
I just recently bought the car, and finally started driving it yesterday, and the only thing I've really done to try to remedy this issue is set the TPS. It didn't change a thing. AFAIK, the only mod that may be relative to anything is a Hypertech chip.
So, my question is...Now what?
Thanks for any help you guys can give!

 

I just did a TPI swap into my Monte Carlo SS and it does this also. I did not think anything was wrong.

Anybody else?

 

Its a normal thing to keep the car from stalling. However, that sounds a little much. Try removing the throttle body from the plenum and cleaning the IAC passages by removing the motor and spraying carb cleaner in there to remove the dirt. Then following the IAC reset procedure tech article on this site when you reinstall everything.

 

Cool. Thanks, guys. My brother used to have an 87 Vette, and he didn't remember it doing that...so mine must be worse than it should be. I'll try it and see what happens.
Thanks, again!