300Sdl intermittent idling spike/drop-off

Now let me try to clarify what the car is actually doing. Normally the problem tends to occur soon after start up. The car starts ok, but during warm up the engine seems to rev up,maybe 1/2 second or so then it seems almost like the engine is going to die, then the motor smooths out and runs ok. The problem also has occurred when the car has been driven and has reached operating temp, the engine cut-off for a few minutes for a brief stop then re-started, and bam you may or may not experience the problem.