You have the M104 inline 6 engine.
I would sugges checking your OVP.
Two other items to check that affect idle quality (other than Vacuum leaks) are the mass air sensor and throttle actuator.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".