CMuc - my name's not Benzmac but I can answer you on this one. A bad strut on my 300E caused exactly the feeling you describe. I was able to swing the rear end left and right using the gas pedal - very scary. I identified the bad bushing by jacking the car up and pushing the wheel around with my hands while looking at all the links. Bought the link for $35 mail order and replaced it myself in 1/2 hour. Put the car back down before you completely tighten the link and then get an alignment as Benzmac says.

P.S. Obligatory plug, they sell parts here!

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Rick Miley
99 E300 TurboDiesel
87 300E
86 190E 2.3