Does the inner lining of the Throddle body have a build up on the surface area? A carbon build up preventing the "butterfly" flap from closing properly can cause problems similar to what you are describing. I however only have experience with several m119 engines on the W140 and W124 models.

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Russell McMahon
Tulsa, OK
2001 CLK 320
1992 400se
1993 400e
2000 320ML