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Engine revs when stopped?

I have a 1997 Saturn, and have noticed for the past couple of months that when the car is idling at a stoplight, the engine seems to rev or almost skip a little bit. The RPMs go from about 1000 down to 500 for a couple of seconds, and this will happen once every 10 seconds or so. Otherwise, it runs fine…but this is happening more and more frequently than it used to.

I had the transmission rebuilt over the summer and its still under warranty. Any ideas of what might be causing this?

The first thing that I would do is to check for a vacuum leak.
If you don’t find a vacuum leak, then the next thing to consider is the Idle Air Control (IAC).

+1 with VDCDriver’s suggestion.
If it is the IAC, you can probably just clean it with some throttle body cleaner. Mechanics will often replace them but they rarely actually need to.
You will want to remove it from the car to do that but it usually removes easily after loosening two bolts, some lines and a connector. Not sure about Saturns but it usually is conveniently located right on top of the engine on the cars I’m familiar with.

@RemcoW I haven’t had much luck cleaning IACs. And that includes several different manufacturers. My philosophy is to try cleaning the IAC once only. If it doesn’t work (and I haven’t had much luck with it), immediately replace the part. It’s usually reasoably priced. You can’t justify spending hours and hours cleaning a part that can be easily obtained for $50.

http://www.rockauto.com/catalog/moreinfo.php?pk=497031&cc=1266847

@asecular are you joking with the foot on the gas pedal?