carman850:
Excessive, steady vibrations in "D" at idle are usually a surefire indicator of engine mounts gone bad. If you can feel rather strong vibrations with the tranny in D when you put your elbow on the doorpanel while at an intersection or so, your mounts need replacing. These cars should idle absolutely smooth in 'D" with no vibrations whatsoever. And to avoid excessive labor, they need to be done sooner than later as the vibrations usualy seize up the upper bolts and it becomes increasingly difficult to break them loose.
Your car shaking at higher speed is a different issue, could be the driveshaft support bearing gone bad or any of the front or rear suspension components. Sometimes loose control arm bolts can cause this. You might also want to check the steering dampner(cheap fix!).
Hope this helps.
F.J.

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F.J.
81 300 SD grey/palomino 168K miles
84 190E 2.3 black/grey 64K miles (wrecked)
85 190E 2.3 maroon/palomino 92K miles
88 300E desert red/palomino 204k miles
(made to look like a '94-95)
92 400E desert taupe/creme beige 120K miles
(converted to 94-95 E420 looks)