Check all the boost control hoses -- they go from the intake manifold to the ALDA and to the transmission switchover valve and vacuum amplifier (and usually some other valves, too) and the boost controller on the turbo. All the rubber ends are probably shot, causing the turbo signal to be lost until the pressure really goes up. Causes the IP to inject fuel as it it were a naturally aspirated engine, then jumps it up about 2000 rpm suddenly.
My 87 is doing this rather badly -- I replaced all the vacuum side the other day, and it now shifts better, but still "lunges" after no throttle response unless I really get on it. I suspect all the hoses -- they have nice little clamps on them, so I've been waiting for some time to get to them.
You might also want to check the condition of the turbo itself, too -- take the intake hose off and see if the wheel turns smoothly and easily. If it is sticky or rough in rotation, you need new bearings. Bad turbo makes these things SLOW until the turbo pops on -- they don't inject as much fuel as the na engines without boost.
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!