Disconnect the banjo bolt and blow down the line. If it doesn't hold pressure, find the leak and fix. The line goes to the vacuum amplifier to the tranny modulator, the EGR controller, and the ALDA -- the switchover valve is a rectangular box, the line goes "through" it on the way to the ALDA. Usual failure is for the interal valve to blow out so boost is always vented out the top. You can temporarily bypass it, but I would fix it personally, it's much cheaper than a new engine....

If the system holds pressure, you need to verify that you are getting boost with a boost guage installed while driving (you won't get any unless the engine is under load).

If you have at least 8 psi boost, you need to adjust or fix the ALDA -- if no boost, the turbocharge is kaput or the wastegate controller has failed open.

Do you get any smoke at wide open throttle?

Peter

__________________
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!