92 300D came with turbo. have you switch from the computer controlled actuator to the pressure controlled one. If the EDS Computer detects any fault it cuts signal that controls the boost/turbo.
Here's the Thread to read:
http://www.peachparts.com/shopforum/showthread.php?t=212097&highlight=wastegate+modification
It's about $100 fix, makes the car much better. You'll think it is a different vehicle. (I drank the cool-aid)