If the Throttle Arm on the Fuel Injection Pump is not connected to the Linkages.

The Governor set up so that the Governor controls it at idle and on the High rpm end. Inbetween that there is no Governor Control.
If the Idle adjustment Screw or the Rack Dampner/Governor Idle Pin are cranked down too far the rack can be pushed beyond the Governor Idle control.

The Fuel Rack inside the IP could be stuck. Not uncommon on an Engine that has sat a long time.

Remove the Fuel Injection Pump Shutoff Valve/Servo and see if that stops the run away. Disconnecting the Vacuum from the the Fuel Injection Pump Shutoff Valve/Servo will not cause it to run away.

However, I am not sure what would happen if the the Fuel Injection Pump Shutoff Valve/Servo where the Vacuum Tube/Hose connects was plugged off.

If someone improperly installed the the Fuel Injection Pump Shutoff Valve/Servo it can cause a runaway.

__________________
84 300D, 82 Volvo 244Gl Diesel