i have a 1997 e320.
i had some issues with the motor idling badly and running rough.
i have changed the plugs and also the coil connectors to the plugs and the car is 100% better.
if i rev it at idle it feels rough throughout the rpm range. you can feel slight vibration thru the steering.
when i drive slowly it feels smooth but as soon as you "floor" it and it kicks back in the gears it feels rough.
i did replace the engine mounts but it is still there. at idle the engine is smooth.
i feel the engine is running smooth now but a vibration is coming through some where.