I am having the same surging problem on my 1993 300e with a 3.2 engine.
So far we (the mechanics that is) have replace the O2 sensor after getting a flat line reading intermittantly. No help. They cleaned the idle control valve out which was mentioned in another thread, no help.
My symptoms are, slightly rough idle when cold, about 20 minutes into my commute the idle starts to surge and the exhaust stinks like the cat is bad. A friend said that might be the car leaning out and the cat "cooking"
There are no apparent vac leaks, and the harness recall was done on the car in the past.
The mechanics had a 1994 320E at the shop that runs fine, so they swapped in the known good Mass Air meter, and there was still an intermittant surge when warmed up.
No check engine light.....
Need more suggestions?
Sold the Benz, sayin' goodbye. Thanks for all the info you guys and girls provided.