Considering I've just been through a bad diesel clogging every filter in 2 cars adventure, I'd aim at the tank strainer first. you could even hook a small pump to the fuel line at the front of the car and tee in a vacuum gauge to see how much flow you get and how much vacuum is pulled to achieve said flow.

Did N/A models not have a bowden cable? I know vacuum on my cars only controls the shift firmness, the points are controlled solely by the bowden cable and road speed.

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1982 300D (w123, "Grey Car")
1982 300D (w123, "Blue Car")
2001 Ford F150 "Clifford" (The Big Red Truck)
1997 Dodge Ram 2500 12V Cummins
1996 Dodge Ram 2500 12V Cummins
Previous Vehicles:
1995 E300D, 1980 300SD, 1992 Buick Century, 2005 Saturn Ion