I was searching and came across this problem. I have this exact same problem in my 500SEL now, does anybody know what could be causing it.
It's great when cold (as it should be), then gradually as it get warms, the engine hesitates and the car seems to shake a little. After a couple of seconds of my foot on the pedal, the engine finally responds at a higher rpm.
I'm totally stumped on this one. Any advice or help would be much appreciated.

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1985 500SEL 124k miles
2001 Honda Civic EX