2002 Saturn SC2 unusual idle cold start


My Saturn revs sometimes over 2000 RPM when it’s trying to idle from a cold start, then drops back below 1000 and will die if I don’t give it gas. Very cold, below 10?, but even at 30?. As engine warms the temp gauge goes down when engine revs and up when RPMs drop! I suspect the Engine Coolant Temp Sensor, as have read it was plastic and would crack on older Saturns and cause the PCM to think it was -40?F!

Is that still possible on the 2002? My mechanic has it in shop and will get to it Monday. Short on time, so want to direct him as his response after duplicating problem today was, “No idea, get to it Monday!”


You’re better off not “directing” your mechanic at all. If he is a decent mechanic, the he is a professional and probably doesn’t really want to hear the speculations of the amateur. (Though he might be polite about that). Just report the symptoms and let him work on it.

That said, a difficulty with a coolant temp sensor could be involved. This is an easy thing to check in at least a couple of different ways.

I don’t think the problem is with the coolant temp sensor. When they fail in that manner the engine RPM’s go high and stay there and doesn’t fluctuate.

The problem might be with the Idle Air Control valve. The IAC valve is what controls the engine idle speed under all conditions. These IAC valves can become sensitive to temperature where they will hunt for the proper position for the idle condition. The engine then idles at a high RPM, the RPM’s drop, and then the RPM’s drop to where the engine will stall unless the gas pedal is depressed. And that’s the clue. If the IAC valve completely closes and doesn’t allow air into the engine, the engine will stall. But if the gas pedal is depressed, this slightly opens the closed throttle plate which allows air into the engine which prevents the engine from stalling.


Yeah, “directing” is probably not a good approach especially from a woman. I’ll just “inquire” about the IAC valve. Tester, you described exactly what the car does. Thank you!

"As engine warms the temp gauge goes down when engine revs and up when RPMs drop!

This part is still a little weird. I have no idea what to make of it though, unless the drop & rise of the temp gauge is gradual. So VickyC, don’t forget to describe what the temperature gauge is doing. You may have two problems.

I did describe that to them, yes. They also reproduced the problem and commented they could hardly get it in the garage! But once it warms up, it’s fine! I drove it 30 miles twice after an ordeal warming it up.

Thanks again!