2001 S60 2.4t, 100k miles. When warm, acceleration and cruising are normal, but when I come to a complete stop (as at a traffic light) there is a "bobble" with the idle. RPMs come down normally to about 750, then drop to just under 500, before bouncing back up to just over 1000, then finally settling back in at 750. When the RPMs drop, it feels like there is a single misfire just before it jumps back up. No codes. I was thinking perhaps a sticky throttle body, but welcome suggestions.

 

Starting off with the throttle body is a good idea.

Misfiring is usually an ignition related issue so that could be the next place to do some testing.

 

Do you also feel a shudder when the rpms change? If so it is possible that it is the upper motor mount. I had the same slight rpm change and shudder, the rubber around the mount was completely toast and replacing it solved my issues. These mounts commonly fail and a redesigned one with thicker rubber is available on fcpeuro for about $50

 

It was definitely the throttle body. Good cleaning took care of it. Now if I could only figure out how I got 35 mpg on one section of my last trip when its never done better than 28 I'd be really happy!