i have an 87 iroc 305 tpi 700r4. i have recently got it running again and back on the road. it was idling ok a few days ago but yesterday it started doing this thing where it drops the idle way down. in park it would be 1000 or 750 (different at different times of day) and would not idle in gear by itself unless you held your foot on the gas.i am not sure what these cars are supposed to idle at in gear, but i think 1000 is just about right.. anything less and it seems like it's on the verge of dying. what should i be looking for?? it just started doing it yesterday at noon. this morning it ran fine, and it started doing it again this afternoon. could the iac be causing this?? how can it be tested? ...the car is running pretty good with the exception of this new problem.

 

sounds like the iacv. sometimes even a gummed up throttle body can do that too. has it recently been extra warm around your area? if there gummed up they tend to act up when the weather changes. anyways. take out the iacv, have it checked at autozone. also the pintle shoulnt be completely sticking out. also clean out that area while your at it. sounds like your idle though. you can also spray your throttle body out with carb cleaner and see if that helps, might just be alittle dirty

 

it has not been really hot out yet.. maybe mid 70's. it does seem like it is doing it during the warmer part of the day though...

 

i had this problem recently as well and it was my iacv that was stuck and not working. but theres tons of stuff that can cause this. but since you said you feel no loss in performance then it has to be some kind of air problem, like a vacuum leak or your idle air control valve.

does it ever turn off while on the freeway coasting?

 

i have not had it out on the highway.. i do not trust the tires that are on it right now and i don't really have the cash to replace them yet. up until just a couple of weeks ago this car had not been registered since 02... so it has done A LOT of sitting. not to mention the tires are what i like to call "bald eagles".

 

I recently had idle problems with my 5.0. I ported the plenum over the winter and when I put it back together this spring my check engine light came on and it idled really high. Im not sure if some gunk got into the IAC when i cleaned it or what. The lowest voltage i could get at the TPS was 1.7 volts and the engine light would go out at high rpms. So i ordered a TPS and IAC. Nothing changed after i installed them til I set the IAC and then I was able to tune in my TPS to get the correct reading. Car runs great now, I'd say your problem is your IAC, i ordered both online through autozone for $75.