So I've been tackling all the problems on my 85 300sd and the last thing I need to solve is the rough idle. I've done everything I can think of.

Head gasket
Timing chain
Motor mounts
Tranny mount
All fuel filter and in tank scree
Air filter
Balanced injectors (1950-2000psi)
New lift pump
Valve adjustment (5k miles ago)
New rack damper bolt
Compression checked out within spec and balanced

The injector balance mad the biggest difference. After I did it the idle is perfect when cold but after i get it nice and warm,like a highway drive, the idle will be rough and shaky.

What should I test next? I heard it could be the delivery valves but they seem impossible to track down.