Unfotunatly there is quite a few things it could be.

Does this happen only when the Engine is up to operating temp?

Could have got a load of bad fuel.

In the meant time if you have the type of Fuel Pressure Relief/Overflow Valve that you can take apart you can try stretching the spring till the spring has a free length of 27mm.

Next air leak. If you have the old style hand primer pump that has the hard plastic usually white knob they are known source of air leaks.
Look at the plastic fuel filter. If you can see bubbles moving through it you are sucking in air on down the line.

I am not sure if somewhere in your throttlw linkage there could be a problem or not.

You might try disconnecting the Vaccum shutoff hose on the Vacuum Shutoff on the fuel injection pump and see if that clears up the problem. If it does you have a problem with the Vacuum Shutoff Valve on the Steering Colum Lock.

Try removeing your Oil Fill cap. If that fixes the problem you are having too much engine blowby.

That is some of them.

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84 300D, 82 Volvo 244Gl Diesel