From my experience with EXACTLY what you are describing, im going to bet ALL money on the Oxygen Sensors....

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My Work:
Mercedes-Benz Manhattan, Inc.
Business Development
536 West 41st Street
New York, NY 10036

-My Garage-
1996 E320: White 118,000 miles ~Dad's Driver~
1996 E320: Green 109,000 miles ~Mom's Driver~
~My Babies~
2000 SL500: Desert Sand 96,000 miles
-Previoulsy Judge Judy's-
2008 E350 4MATIC Sport
-Flint Grey/ Ash/ Black Birds Eye Maple-