My 1990 300TE wagon, and my wife's 1988 300SE have the same problem, but the wagon's is more pronounced.
The car almost always hesitates coming off idle. If the car has been used daily, it keeps running. However, if the car has not been run for several days it will hesitate to the point that it stalls (usually after driving several miles, then slowing for a stop-sign. The initial start-up is fine.). It will not re-start until after it has sat for 15 minutes or so.
I replaced the over-voltage relay on the '88, as it had an different stalling problem (usually at high speeds), it solved that particular problem but not the hesitation issue. Thanks everyone! Erik