Picked up a 300,000+ mile '93 300D, have some questions.

[atikovi]

The paint, body and interior are in quite decent condition, as nice as most with half these miles. Found some mechanical issues. It has a bit of a rough idle but smooths out when you step on the accelerator. On a short drive around the block I noticed it's quite slow to accelerate, no turbo kicking in and no turbo wooosh. Under the hood at idle I hear a kind of compressed air leak. Its like a puff puff sound 2 or 3 times per second. The transmission upshifts harshly, kinda snaps your head back when it shifts. And the tach is inoperative. Any first thoughts?