My roomate's car is overboosting, and sometimes hitting fuel cutoff. This is rather violent in the low gears. I'm trying to understand why it is overboosting like that. I'm also curious about this because I'm going to have my first ever turbo motor in my Audi, and I really dont know much about turbos, aside from how they work.

disconnect wastegate rod from wastegate falp see if flap will move very common for saab to sieze wastgate rod in housing sometimes with lots of penetrating oil and light tapping with hammer will free it

That's what it was... the turbo had a bent fin too, so it's currently being rebuilt