Turbo Guage/turbo issue
 

ok, so lately I noticed my car ('93 940 Turbo) is running a little sluggish. its also making a strong vibration noise, kinda like the droning of a prop airplane engine that happens between 2000 and 4000 RPM. It happens if the car is in drive, neutral or park, on the highway or side streets. Very annoying. Also, recently, I noticed a black ring of deposit around my tail pipe, not sure what that's about. But its the sluggishness of the engine response that is most annoying, and I noticed that my turbo boost gauge is only going into the white area about 1/4 of the way when I floor the accelerator, when it used to go all the way into the white. Now, the question is, would it more likely be a problem with the turbo, given the other symptoms? or would it be more likely that it is the boost gauge?

Does one of the pipes going from the turbo to the throttle body have a tear in it?

Unfortunately, no. There are no tears in the hoses from the turbo to the TB.