Your profile shows a 83 300D. Rough idle could come from the valves out of adjustment. When were they adjusted last?
The fuel injector rack also has a part, a small brass piece whose job it is to dampen the rack. These often need replacing on older cars.
Clogged injectors can also contribute to a rough idle .... as well as bent or bad valves, bad fuel injector pumps ..... also a bad engine mount ..... etc.
How many miles?
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)