With my 300SD, I noticed that when I start the engine from sitting overnight it will sometimes surge a bit. What I mean by this is that the RPMs will start out around 600-700rpm for a second or two, then drop down to about 500 for a split second, then back up to 600-700. This usually happens one or two times, then it evens out. You can feel the shakiness in the car when this happens. It has the feeling that a manual transmission vehicle has when it's about to stall.

The engine runs normally and usually has full oil pressure within a second of the engine starting.

The surging doesn't happen every time either. It's completely random.

Any ideas?