Originally posted by suginami
I have a 1993 300E and had a surging idle similar to what you are describing.
Common causes of this sympton usually are:
1. mass air flow meter
2. vacuum leak
3. throttle actuator
My problem in the end turned out to be a vacuum leak at the intake manifold. My crack mechanic figured this out after changing a $961 actuator and a $250 mass air meter.
Did you keep the old, now known good actuator? If it turns out to be the part I need I will buy your old one.
Sold the Benz, sayin' goodbye. Thanks for all the info you guys and girls provided.