My 88 420 with 149K has a slight "rock"
when I first turn it on: hot or cold start.
Its had this for a long time. MB dealer said I needed a valve job- that was 45k miles ago. Second MB dealer said it needed valve stem seals. That was done- car ran fine since. No more burning of oil.
The rock continues but diminishes slightly as the car is driven. Once in a while it will run perfectly smooth. Most of the time it has this "rock"- more obvious in neutral,
less in gear. 150K serivce has been done. Always dealer parts. Engine is smooth on acceleration and never misses, stalls, hesitates. Any suggestions?