Need help, I have a 94 Camaro Z28 that I've owed its whole life. A few months ago it started idling up and down ever so slightly, but I could tell when stopped at a red light. Then after this last cold spell it idles between 600 rpm up to 1500 rpm and sometimes it will idle down enough that it dies. All stock, It has new injectors, fuel regulator, fuel filter (Last year). I've replaced the Idle control valve and MAF sensor hoping that would fix the problem, but no luck. All vacuum lines seem to be fine, Still has original Opti-spark. Any info would be appreciated.

 

Auto or manual transmission - affects idle RPM programming? Idle RPM is dependent on coolant temperature.

 

Its an Auto

 

Nothing is jumping out at me. A couple years ago I believe you changed out the coolant temp sensor. The PCM uses coolant temperature to set the idle speed. In really cold weather idle can go as high as 1,200 RPM. As the engine warms up idle speed with manual transmission should drop to 800 RPM (above 111 degrees). Shouldn’t drop below that. Faulty coolant temp sensor shouldn’t cause it to go as high as 1,500 RPM.

Did solve one case of wild idle speed changes. Turned out appeared the epoxy insulation in the MSD Opti cap was breaking down, and inserting a spurious pulse in the optical sensor output. The ECM (93) thought for an instant the engine was running at 7,000 RPM and started opening up the IAC valve, as it normally does in response to increasing RPM, and idle speed was reaching 2,700 RPM. I used a Scan9495 data log to find the pulses and the IAC responses. But I don’t review data logs any more.

Wild guess…. check the throttle cable to see if it came loose and is allowing the blades to “flutter”.

 

Yes I did change the coolant temp sensor and it seems to be working. I've discovered several vacuum leaks around the throttle body and a hole in the underside of the intake boot. Gonna see about replacing the boot and throttle body and see where that leaves me. thanks.