No, not the rack damper bolt. You would have the problem any time the motor was at full operating temperature, were it that.
Diesel911 has raised one possibility, another would be that some component of the injection pump is out of spec and after you shut the car down, the resulting "heat soak" (absorption of heat from the motor by the pump) is aggravating that.
My '79 SD had a similar issue and various mechanics either indicated the governor inside the pump, or something to do with one of the pump plungers.
The problem was 'solved' when I installed used motor after the timing chain snapped on the original motor
