Questions and Answers

Chevy Lumina Weird Idle Q. Mr. Ciulla, I have a 1993 Chevy Lumina Z-34 with a 3.4 liter engine, automatic transmission, fuel injection, ABS, P/S, A/C, cruise with 87.600 miles. In November, the engine died while going down a mountain. It started back without incident. We then added gas treatment.

Then in December it started overheating. We replaced the thermostat, then the radiator. Almost immediately after the radiator was replaced, the car started idling too fast when it was first started. We took it to the garage and they cleaned the valve that regulates air flow and checked the intake manifold gasket for leaks. While replacing the manifold gasket it was discovered that a small plastic piece on top of the motor that has vacuums hoses hooked to it was broken, so that was replaced.

The problem worsened. It sometimes idles as high as 3,000 rpm's and at times misses as if you were pumping the gas. The weirdest thing is that when it idles too fast holding the brake pedal down lowers the rpm's and pumping the brake increases them. The biggest problem is that it does this intermittently. It will start fine for a few days then mess up.

Sometimes, if you turn it off for a few minutes then restart it, it is fine. Once it warms up it runs great except for a slight miss occasionally when you accelerate at around 60 mph. By the time we get it to the garage it is running fine so the scanner doesn't detect any problem. We have left it at the garage for a couple of days but it won't act up for them.

They have replaced several hoses, the MAP, and cleaned some valves including the PCV valve. Nothing helps. Do you have any idea what the problem could be? Any information you can give me will be greatly appreciated.

Thank you,
Lois

A. Have they tried replacing the ECM? This sounds like a definite possibility. When they go bad all kinds of strange things happen.