Questions and Answers

Lumina Stumbles

Q. I have a 1995 Chevrolet Lumina van. 3.1 liter V6 throttle body injection. auto trans. 58,000 miles.

While driving, the engine seems to stumble. It quickly returns to normal but then it will do it again, repeatedly. This only occurs between 30 and 40 mph. It accelerates normally. This happens whether the engine is cold or warm. It has never had a problem with overheating.

I have replaced the fuel filter, transmission filter, air filter, pcv, plugs, wires, rotor, and cap. The check engine light never comes on except at startup as appropriate. I have run some injector/carb cleaner through the gas.

Soon I will have snatched myself completely bald. Please help.

Thanks,
Rob

A. I would check the Throttle Position Sensor. If it happens at that one particular position, you probably have a bad spot in it. The TPS is a variable resistor and when they get a "dead" spot, it will do exactly as what you describe. It won't throw a code because the reference voltage is still good. Also the computer will only detect an electrical failure, not a mechanical one.