I don't know of any particular problems with the 1990 model 2.5 engine. It has LOTS more power and better fuel economy than the 1985. I have one of each.
The vibration is probably the engine mount, but whatever it is, it is not typical of any MB engine in good shape. This may or may not be a good car for you. It is 18 years old, after all.

The 1985 is easier to work on, but the 2.5 turbo does not require valve adjustment every 10K miles or so. My 1990 leaks oil more than the 1985, but that is atypical as well.


Good luck in any case.

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Semibodacious Transmogrifications a Specialty

1990 300D 2.5 Turbo sedan 171K (Rudolf)
1985 300D Turbo TD Wagon 219K (Remuda)

"Time flies like and arrow, yet fruit flies like a banana"
---Marx (Groucho)