just bought a 90 iroc,5.7,tpi,auto. It ran rather rough so I tuned it up this weekend plugs,wires,pcv,cap,roter. k&n air filter on order. It runs much better. After it has warmed up than you come to a stop and it idles in drive or OD the idle is eradic, from 450 to 650 rpm. Put it in neutral or park than nice and smooth. Its only after the car is warm, it runs great and idles smooth b4 its up to temp. HELP

 

Did you clean the TB and IAC air passages as part of the tune up?

If you can check fuel pressure, make sure it is adequate.

If the oxtgen sensor is more than 30,000 miles old, you might want to check the signal from that as well.

Make sure there are no vacuum leaks. That includes the hoses, brake booster, EGR valve, injector 'O' rings, and gaskets.

 

thanks I will try that. what would explain why it idles perfect in warm up, and perfect in neutral or park. Its only in drive when the idle gets eradic.