1988 Chevrolet Corsica 2.8 idle problems
 

Hello. On my 88 Corsica with the 2.8L V6 i have an idle problem. When it warms up, and i rev it up, and let go of the gas, the idle drops sometimes to 800 - 500 rpm and goes back to 1k rpm. But sometimes it drops even lower than 500rpm and the engine stalls. When i turn it back on right after that, the idle automatically goes up to 3k rpm and slowly drops down to 1k
What could that be? Replaced a leaking brake booster and installed a new O2 sensor, because it was running like that before also
Greetings

Did it just start doing this all at once?
Disconnect vacuum lines one at a time from the ENGINE, and plug off. Process of elimination, and I think also vacuum leak.

Hello. It was doing that since i got the car. It was owned by a collector who barely drove it, it was more sitting than anything since the last 10 years.
It had idle issues before, but they were most likely caused by the broken brake booster. It was rusted through because of a leaking master cylinder, also the brake pedal was hard when the engine ran. It ruined the engines idle a lot, this is why i replaced it.
But now there is still this idle issue. I'm sure i could drive like that, since the idle wont drop that much while driving, but i still wanna get it right.

So you guess its a vacuum leak? I almost thought so. It takes a while for the heat to change in the car. When i switch from cold to hot, it takes like 10 seconds til its finally adjusted

Has anything in the air intake (i.e. filter, tubing ect.) been altered? I had an 88 Corsica new (loved that car) trying to go back in time and visualize that engine setup. My suggestion was to check individual vaccum lines for leaks. If you have a vacuum gauge, see what the manifold vacuum is at 700 rpm.

You can remove, and plug all vacuum lines external engine, see if that is a problem with a vacuum leak.

I'm not sure if the heater valve is vacuumed controlled, just cannot remember, if it is, and what your posting with the heater, I'd suspect that. Again, either remove all external to engine vacuum lines, check the idle rpm, or individually do the same.

Hello and sorry for the late answer. I did get myself a fog machine and was able to properly test for vacuum leaks. And it seems like that i found a leak very close near the intake. Actually its coming from the EGR Valve. As i was blowing fog into the brake booster line (without pressure !!!! just blowing in fog), i could see fog coming past the little rod on the EGR valve.
https://cimg4.ibsrv.net/gimg/chevrol...e67596e72e.jpg

I don't think that fog should get past this rod, correct? And like i said, i didnt even pressurize the vacuum system, i just blew the fog in there.