Yep. pull your plugs and you will see the rearmost 2 are heavily fouled.

You have 2 options- stem seals- about $400. BUT, some mechanics won't do it because they might not last long.

Valve Job- I paid 1800, but would attempt it myself if I had a second car to drive.

Until you get the car in, just replace those fouled plugs to keep the car from missing after idling. Its only going to get worse.

Mike

__________________
'90 300SE 298k
-300K and it gets put into retirement.
'80 300D 255k Purchased new by family in 1980.

Had a:
1973 220 (gas)
1980 300SD
1992 400E