Car revs to 1000 RPM then drops when idling?
My car sputters, and noisily revs up to 1000 RPM then drops to about 500 RPM and then revs up to 1000 RPM again. It takes about 10 seconds each time to do this. The car shakes a little and worsens each cycle the longer I have to sit at a light. There's no Check Engine light on. None of the lights on the dashboard are on. It's a little automatic 2002 Ford Focus ZX3. I know there could be numerous problems, but could anyone happen to guess what it could be?