[Laird Scooby]

I'm not sure so i'm assuming (not always a good thing!) yours is a 940 with the B230FT engine?

Having looked at my main source of reference for cars i either don't know or don't have a Haynes or genuine WSM for, it appears the normal (unregulated) fuel pressure is 3.5 bar, regulated to approx 2 bar with the engine running.

Based simply on that evidence, i don't see that only having 2 bar to start with is going to cause major problems all the time. It could be something as simple as a blocked fuel filter, lazy pump or similar or possibly a dodgy fuel pressure regulator.
Before you proceed any furtherr, i would ask the garage to clarify whether they tested the fuel pressure with the engine running or not, if it was running, was the vacuum hose connected to the fuel pressure reg and did they take the reading from before or after the FPR.

Not being negative but it sounds a little like he's thrown you a red herring to buy himself time to fiddle and try and find the fault or an excuse to fit something you don't need in the hope it will fix the problem.
Could also be worth consulting the Haynes book for your car and/or a Volvo dealer for clarification on the correct fuel pressure readings.