It has been some time but I believe I remember it was helpful but not the full cause of power loss... I found that I had a loose clamp on the rubber boot just outside the air filter housing shich reduced the suction power necessary to open the air flap in the air filter housing ...this was one issue and if you have done the wastegate mod then you do not need that flap to operate as in factory spec so just pull the plastic cover off the air mass sensor ( air filter body ) and reseat the spring retainer inside to remove the spring load on the flap thereby keeping the flap open and allowing full air flow for the engine... this was really the single biggest help toward returning the power...but all in all though it is very fuctional it has never returned to the awsome power it once had...
best

Reading from remote

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'84 300SD sold
124.128

Could be caused by car not getting enough fuel. Have you ever cleaned your fuel tank strainer? Mine was clogged with algae.

As to your black smoke problem, it could be because your injectors are messed up. They're giving fuel but not in a usable mist. They could be just dumping fuel in that can't be used, so it goes out the other end as smoke. Just an uneducated guess.

jeff