When you say that the car idles rough when in traffic, do you mean the car idles rough when the car is stopped and idling?
Or, do you mean that you enginen runs rough when moving at a slow speed / stop and go traffic?
Do you still have oil consumption? If so, could be worn valve guides, but the dealer should've checked for that.
Idle problem could be a stuck EGR valve.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".