If it was just a vibration, I was going to suggest it was your motor mounts.
But since you describe it more as a shake / jerkiness / surging, it sounds like the car is misfiring.
Sounds like you might have a bad connection between one of the three coil wires and the resistor boot.
Do you know if your engine wiring harness has been replaced? It causes all sorts of weird problems. Degrading insulation is a problem on '93 to '95 E320's...
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".