Pontiac Repair: 2000 grand prix rough starts/ rpm spikes, mass air flow sensor, throttle position sensor

Question
my grand prix GT (3.8L) seems to hunt for correct idle rpm on startup after it has already been running for long periods earlier in the day. will spike to about 1500 rpm 2 or 3 times before settling under 1000. Also more recently the car will rev with the brake on at a red light or when cruising at highway speed. Sometimes it will hesitate on acceleration as well and then rev up. Could this be mass air flow sensor or throttle position sensor? Computer gives no codes so far.

Answer
Hi There:

I think your on the right track. unplug the MAF and drive it. it will hesitate a bit but once the hesitation is gone while accelrating see if it runs and idles correctly. If so you found the issue. You may want to also clean the throttle plate and throttle body the have a tendency to carbon up. You may want toalso take the idle control valve out and clean that off as well. good luck :)


Oh one last thing the service engine soon lamp will come on with the MAF sesor unplugged and once you plug it back in and or replace it if indeed that was the issue then it will take a few drive cycles before the engine computer will turn the lamp back off.