Originally Posted by brickhead
my daily driver is a 2002 Grand Prix. the car has 125,000 miles on it. a couple of weeks ago, i started having problems where the rpms would start to flucuate between 1700 and 2200 while i was driving. this only happens for a few seconds after the car is in 4 gear and i am doing around 45-55 mph. then it will run normally, but it will do it again if i slow down a little bit and try to accelerate again. i did a tune up, changed the fuel filter, changed the trans filter and fluid all at 100,000 miles.
i plugged it into my handheld scanner, but it didn't show any faults. i took the car to the trans shop today and they said the trans is fine, it has to be something with the engine.
any ideas ???
thanks in advance for any info you can provide.
Check B+ line voltage, if the alternator isn't keeping operating voltage up, the computer will cause the tranny to hunt in and out of converter lock up as well as in and out of overdrive.
On the engine this can be an IAC problem where the idle control motor is hunting for it's proper opening, this is usually the result of a poor or missing road speed sensor input to the computer, this can also be a sign of low B+ voltage. This usually will not set a code. The IAC usually shows as hunting in cruise, or dropped idle speed and stalling when coming to a halt, or as a hesitation when the throttle is opened after coasting down in gear some X amount of mph, then re-accelerating to cruise speed again.