Slight stumble at idle in gear
 

My 1978 300D with the OM617 seems to develop a slight miss when in gear while stopped once the engine is warm. If I put it in neutral the miss will go away, also if I give it any gas it seems to run normal again. Any ideas on where too start with this one.

Possibly the idle speed is too low making it feel like there's a miss when in reality it's just rough.

Possibly worn motor mounts that are allowing vibration to be transmitted into the chassis.

Maybe even a combo of both!

Do the NA pumps have a rack damper? I don't know.

I'd put a can of Techron injector cleaner or Lubro Moly Diesel Purge in the fuel tank and run that through to see if it clears up the problem, and then you know that your injectors were probably the culprit and will need attention.

If money and time are not a concern, pull the injectors and send them to Greazzer for clean/test/adjust, I think his price is about $100 which is a darn good price and he's got a great reputation.

These are also likely / possible.

My '85 euro wagon with NA engine did not have one, so I'm doubtful this car does.