2003 Chevy Cavalier: Why does acceleration sometimes stop working properly?

Question

Sometimes when I'm driving, when i press gently on the gas pedal [like you should be doing] the acceleration doesn't work at all, and when i press down on it harder it works and revs violently, and then the next time i stop the acceleration stops working entirely and the battery light comes on. I have to restart the car to get it work accelerate again, THEN the gas feels like it normally should.

I already took it to some very reliable auto mechanics I know, and they can't diagnose it because >95% percent of the time, it works just fine.

I removed the battery and took it to a local battery dealer, and they said the battery is just fine and that "the accelerator could be failing to power the battery", so they tested that and it was just fine. The owner was telling me it might be the PCM (powertrain control model).

More theories please?

Answer 1

I would start by testing the full sweep of the Throttle Position Sensor (TPS).

These can go bad in a way that creates intermittant problems. The wiper area of this "potentiometer" can wear, especially around the idle position, and create all sorts of havoc with driveability.

This can occur without throwing a OBD diagnostic code, because the PCM has no way of "testing" whether the information it receives is valid.

The test procedure is simple if you have a digital voltmeter. With the key on, but engine OFF (not running) you slowly manually move the throttle and observe the voltage at the sensor. It should change smoothly with no sudden jumps or leaps. It also needs to return to the same fixed value every time it returns to idle.

If you have a scan tool with a PID capability, you can also do this test without "backprobing" the sensor. If you can observe Throttle % (again, with key on engine off) you can operate the accelerator smoothly and observe the realtive change in the Throttle % PID.

This test may need to be repeated a number of times to catch a failing TPS.

Good luck!

Answer 2

I would agree with the TPS suggested earlier except for the mention of the battery light coming on. Assuming this is not because the car has stalled, I would wager your car's electrical system has a bad ground. The negative battery cable can look fine but have lots of corrosion internally. Replace it with a new one, but I would go one step further and try to find a generic replacement cable that has two cables coming off the battery clamp. One lead you attach to the OEM location, the other to the car body. I've fixed an similar intermittent issue by attaching the second lead to the strut tower using one of the existing three nuts there. An unpainted surface would be even better. Go ahead and replace the positive cable as well while you're at it (with a standard replacement).