Check for vacuum leaks -- brake booster line, brake booster itself, all the emissions stuff, and tranny control. Also climate control -- does the AC tend to blow up the windshield instead of out the dash vents?
Idle control valve hoses go bad and leak, causes rough idle, stalling sometimes, and throttle lag. You should have decent response even in 2nd, if you put the throttle down and ......then it goes, you have either an overlean condition (also check OVP relay, it can cause mixture control failure problems), a bad 02 sensor, or a vac leak (or combination).
Worn out secondary ignition parts will do this too, as will a bad vac signal line to the computer on the driver's side fender!
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!