83 300D idle rough under load
 

Car at temperature, shakes when A/C is on and in drive with brake depressed. If I turn off A/C or put into park then car smooth out. I turn up idle speed a bit and it helps but don't want to turn it higher than necessary.

Any idea? What could cause it? What is the normal idling speed for the OM617?

Are you still running the stock Rack Damper/Governor Idle Pin?

You might try re-adjusting the Rack Damper/Governor Idle Pin.

Someone had a similar issue on but on a 240D. On the MW Fuel Injection Pump there is another adjustment after you remove the cover. It has to do with the sensitivity of the Governor to catch the load. On other Diesels it is called Governor Droop.
I think there is also another idle adjustment.

However, I think I read it over on Benzworld.

Over on the superturbodiesel forum there is info on what adjusting the stuff under the Governor Cover. I believe it is ForcedInduction that has some pic with labels on adjustment places and what they adjust.