My first thought is that the engine is either low on oil, or there is restriction somewhere around the pick up, like maybe heavy sludge buildup.

Has this car had frequent oil changes, is it used for a lot of short hops?

Good luck,

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Larry Bible
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles