You will need to have the pressure and differential pressure check on the fuel distributor before condeming the regulator.

Rough idle with normal operation off idle is either the throttle position switch or a vac leak nearly all the time -- failures of the pressure regulator or fuel distributor are almost never idle only.

Vac lines are a good place to start -- also, I'd check the fuel pump relay -- if it's hot, replace it. This cured most of the rough idle on my TE.

And, it could always be a dribbling injector -- this will cause one cylinder to run way rich at idle only, and since you have feedback control of idle mixture, the computer will happily run the rest of them lean. Problem goes away off idle since fuel delivery off idle is pretty much normal. Check the plugs for signs one cylinder is running rich all (black or dark brown insulator tip).

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!