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 …

Car revs up and down while idling

mcparadise July 7, 2007, 1:38am 3

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.