1

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?

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!

  • Thanks again, i've been looking into diagnostics. When I turn the key on, other than the battery light, i see a picture with a downward pointing arrow in a (water tank?). It's not the engine light cuz i know what that looks like. – thinksinbinary Nov 22 '17 at 21:22
  • Sorry; dunno. A picture would be worth like 786 words (given todays word inflation value...) – SteveRacer Nov 23 '17 at 6:16
  • I looked at an owners manual and the light indicates low amounts of coolants, possibly a "serious overheating problem" my.chevrolet.com/content/dam/gmownercenter/gmna/dynamic/manuals/… i guess it may have nothing to do with throttle sweep or potentiometer...its no wonder that often auto mechanics dont know what they are talking about. – thinksinbinary Nov 24 '17 at 0:42
  • I totally resemble that remark. I have no idea. (What do you call a blind deer? No-eyed-deer...) It's just where I'd start looking if it were my car or my customers. I've lived this scenario before. Check the TPS and right or wrong, that's another step... Best of luck. – SteveRacer Dec 1 '17 at 7:58
  • thanks steveracer, i got my OBD-II diagnostic scanner in the mail today, it's saying that the problem is an oxygen sensor or vaccum leak. autocodes.com/p1133_chevrolet.html – thinksinbinary Dec 1 '17 at 21:19
0

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).

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.