I had a european 500 with a running problem one time ( slow doggy acceleration ) checked the c/o etc . Well ended doing a backpressure test and it was so small of a cat was installed on the car. Had a 560 cat put on and the car ran excellent. Something to think about.
Mercedes Technician 7 Years (retired to Hyundai)
2000 Dodge Durango
98 Mazda truck