What Barry said was to disconnect the Vacuum Line from the Vacuum Shutoff Valve on the Fuel Injection pump and plug the Vacuum Line.

That means there is no way Vacuum can have an effect on the Vacuum Shutoff.
If you drive the Car and there is still a loss of power the power loss is not being caused by Vacuum getting to the Vacuum Shutoff Valve.

If it is stull Slow Check your throttle linkages at the Fire Wall. There is a Rubber part that rots away and some have a Big Plastic Ball/Bushing unseen behind the Bracket that crumbles away.

Or simply hold onto the Fuel Injection Pump Throttle Lever and have some one step slowly on the Accelerator Pedal and watch the movement of the Throttle Linkages. If there is a lot of slop in the linkages try to find the cause.
In the Manual there is specific lengths for the linkages.

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84 300D, 82 Volvo 244Gl Diesel

Thanks everyone for the contributions... I will try to swap the vac lines at the back of the switch and see what happens.

Regarding the loss of power, I don't believe the linkages are at all related (correct me if I'm wrong here...) because the loss of power only occurs when the car is in gear (and intermittently at that). If I put it in park and push the pedal down the engine responds normally with plenty of power. To me, that seems to rule out the linkages right? ...because it only occurs when in gear?

Zacharias: I checked the pressure sensing line and it looks good, no cracks of any kind..

Not really. You only have to deliver a small amount of fuel, to rev up the motor while in park or neutral. While driving on the road, under load, you need much more fuel, hence you are pressing harder on the pedal and moving the linkage further.

I suggest you swap those vacuum lines at the switch and get that sorted, then report back if has made any difference to the performance problem.

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

my vote,,,

The no power issue could be that the shutoff valve is getting some vacuum and not allowing the IP to throttle up. Shutting the car off releases this vacuum sometimes,,, just a guess

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Closing the store
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