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.
'90 300SE 298k
-300K and it gets put into retirement.
'80 300D 255k Purchased new by family in 1980.
1973 220 (gas)