My 87 GTA with a 350 TPI varies the idle speed 200 to 300 RPM and I keep getting an service engine code for a faulty O2 sensor. I changed the sensor but the code keeps coming up. I have an 89 Corvette PROM in here which I bought from TPI parts. Recently I found an emissions hose with a crack on it that attached to the side of the plenum. I replaced that as well. Still the idle races a bit with either the transmission in drive or in neutral. I'm wondering if some type of advance is occurring at the distributor. The ICM is new also so this should be good.
Any ideas folks?

Thanks,
Laser

 

Replace the EGR valve.

 

Thanks, that was done about 3 years ago when the top of the engine was rebuilt. I just run synthetic oil so it should not be crapped up in there. The code is a 13. I replaced the O2 sensor and the IAC valve also. Runs pretty smooth but intermittently the idle rises and lowers up to 200 RPM. Nothing is moving throttle wise so either fuel or electronic advance is going on. The ICM is new also but the distributor is the original. Coil is new also so there aren't many things left to replace.

Regards,
Laser