Is there a manual idle adjustment near the fuse box under the hood? I was going thru old threads and found a post that mentioned a numbered knob, or plastic thingy to raise or lower the idle a little. After warmed up while driving(or parked), the idle goes down to about 550 rpm. The book says it should be 670 +\- 20 rpm. Also when revved and let off, it drops to 500, then up to 550. It's kinda rough that low. I have a 1990 300D 2.5.
Thanks aplenty.