Check the idle control valve hoses. One of mine was loose it was so hard, and if seriously adrift, you will have screwy response to throttle. I once left a hose off on my old Audi Fox, and had exactly the same problem -- would only run if floored.
I don't think you will have the other problem I had with the Fox -- ice accreation in the venturi in cold weather. Fuel control flap would rise until the car would only run at full throttle -- trailed black smoke behind. Cured by disconnecting the blowby hose.
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!