1989 190 E Car Vibrates When in Gear
 

What could cause the car to vibrate when I put it in reverse and also in drive?

The vibration stops when the car is in park with the motor running.

That would be your motor mounts my friend:)

Just diagnosed the same symptoms on my friend's 124 last weekend.

Exactly the same issue - engine vibrates in gear.Popped the hood with my friend in the driver's seat and saw the engine/air filter housing vibrating severely in the engine bay.

Motor mounts!