I noticed on the drive home that something was amiss. When I drop off the throttle to idle, it bounces between 500 and 1000 rpm continuously. The frequency of the bounce is about 1hz, and it never goes away. To add to the issue, it only does this when the car is moving. When I come to a complete stop, it immediatly goes to a rock stable idle at 900rpm (right where is usually idles).
The performance is not affected at all. I just did a quickie G-tech quarter-mile run, and got a 14.3 second run, which is just a bit faster than average for my car.
Who has a theory as to what this bouncing idle thing is all about?