First post. Please don't kill me.
Hello.

I just purchased an 760 Turbo Wagon from 89. It has the usual issues with OD relays, sagging headliner, drained A/C, and warped front discs. This is all fixable.

The turbo, though, baffles me completely.

Below is an attempt of a symptom description.

MPG: 10-12.

Turbo gauge hits 12 o-clock immediately when I touch the gas pedal.
If I keep the gas pedal pressed down, the gauge progresses into the middle of the white field (1:30-2:00) within 2-3 seconds. A hiss is also heard, which I believe is the wastegate.

There is, however, no turbo effect whatsoever. If I put the shift lever into 1 and slowly press down the accelerator to make the turbo gauge climb, I acually lose a small amount of acceleration when the gauge passes 12 o-clock and the wastegate starts to hiss (which it does exactly at 12).

There is a small lateral (radial) play in the turbo shaft. Nothing big though. Some oil sweat around the turbo, but not dripping in any way.

The intercooler and hoses surrounding it is new. I tightened up all the clamps to be on the safe side. No obvious leaks detected.

The hose going from the MAF sensor (just after the air filter) down to the turbo intake was rotten at the turbo end due to oil contamination and was probably leaking. I fixed it temporarily with duct tape for now . (The 10-12 MPG was measured prior to this fix.) The fix did not change turbo's behavior in any way.

The small hose from the turbo to the intake manifold is not clogged.

I have not checked if flame trap and oil separator is clogged.

I have not checked if the cat is clogged.

I have not checked the fuel filter.

Air filter and spark plugs looks OK.

Apart from this the engine works fine. Starts nicely when cold and warm. Idles evenly. No weirdo noises. No stuttering or other misbehaviors.

And now the question:
What is wrong with my turbo?

Thanks in advance for any tips and hints!

/Magnus Feuer.
Costa Mesa, CA.