A large volume of fuel passes through the fuel injection pump housing and that keeps it reasonably cool.

Only a small amount of fuel enters the injectors and only a small amount of that fuel lubes the injector and comes out of the small return lines.

Do you see any air actually moving through the plastic fuel filter and if you can see through it the line from the Fuel Supply/Lift Pump to the secondary Spin-on Fuel Filter?

"(new injectors, filters, primer, service delivery valves, injector pump)" how much of that can be proven to be true?

Raise your idle speed to 850 rpm using the proper idle adjustment screw on engine block side of the Fuel Injection pump.

Do a valve adjustment.

Back out the Governor Idle Pin/Rack Damper Bolt and adjust it. Not despite one of the names it is called it is not the idle adjustment.

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84 300D, 82 Volvo 244Gl Diesel