Just an idea, but on other Mercedes engines, when there is a surging / fluctuating idle, some common sources are:

1. throttle actuator
2. mass air sensor
3. vacuum leak (which may give you bad codes suggesting that either / both numbers 1. and 2. are bad).

If your car is missing, a common source is a bad spark plug wire or bad boot.

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".