My 83 300SD Runs smooth as silk when cold outside and cold engine. As the temperature outside increases than so does the rough idle. To break it down here's how it runs.

cold (below 50 degrees)/ cold engine = smooth idle
cold (below 50 degrees)/warm engine = slightly rough
warm (above 70 degrees)/cold engine = slightly rough
warm (above 70 degrees)/warm engine = very rough

Any suggestions?

 

Maybe motor mounts.

 

Thanks. That was the first thing I did. I also replaced the engine shocks too while I was at it.

 

If it's an even shake when running rough warm I would say the rack stop on the back of the injection pump needs adjusted or replaced. This stop keeps the inj. rack from shaking at engine idle. It's been awhile since I adjusted one , I think it's a 14mm nut locking down a 12mm adjustment sleeve. Turn it in a little and try it. If you go too far in it will cause some running problems or no start. In that case just back it out, it won't damage anything. I've also seen these wore out and needing replacement but ussually just adjusting them fixes the complaint.