Could have a damaged wastegate valve and its bypassing exhaust. If you have a hiss that you didn't hear before, money says finding that will be the problem. All your induction gaskets & O-rings good? Is the turbo inlet restricted? If you still have the air flow meter, make sure the vane is free, or delete the thing and all the EGR garbage. One other idea is seeing if a local shop with a smoke machine can hook up to it and test it for leaks. The shop I used to work at had one and it was the cats meow for finding induction system leaks. Sucks those machines cost so much.

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87' 300D, Currently undergoing an OM606 swap/build! SUPERTURBO!!!
03' 2500HD Dmax + goodies!
82' 300SD, parting out!
93' 300TE 4matic, parting out!
83' 240D Project Cheap Drive
89' 300E, parting out!
74' Datsun 510 wagon
88' RX7 10thAE, 13B track car build soon

Skippy~ As for perception: Drive what you like and can afford. Those who don't like it can supply vacuum to one of your components. LOL

If you need parts, I have some!