Car revs up and down while idling



My 2001 Isuzu Rodeo Sport (65k miles, auto transmission) sometimes revs up and down (from 500 to 2000 revs/min) while idling in Park. When it does this, putting it in Drive causes it to shudder as if it’s going to stall, but once it gets going, it runs fine.

This doesn’t happen every day, but it doesn’t seem to be related to the temperature. And it only happens after the car has sat overnight. I fear that this portends bad things to come. I imagine that the gears may be slipping, but am not sure. I have recently had a transmission flush, but that doesn’t seem to have made any difference.

Any idea as to what might be wrong?


Sounds more like a vacuum leak or an engine sensor going bad. This doesn’t sound like a transmission problem at all.


I agree. I’d look for a vacuum leak first. The transmission “flush” you had may cause problems down the road, but the transmission is not the cause of this particular problem.


Thanks for the response. So is there a way to make this happen consistently so I can show it to a mechanic? Otherwise I won’t even be able to verify that the repair fixed anything (until some time later by when the mechanic will have absolved himself of all responsibility.)