I just installed a vdo boost gauge in my 95 turbo 850, mainly to find out why and how much boost i'm losing. I recently replaced 3 vac hoses *(all the ones attached to the airbox)*, and i tighted all intercooler hoses, and this did help the boost alot, but now I'm having another boost problem. When i WOT and downshift from a higher gear into a lower gear, it spikes right to 15psi, and then the boost falls to like 5psi, then very slowly builds back to 10 slowly. Also, sometimes when i just WOT throttle, the gauge shows 10psi, but it doesn't pull as hard as other times. My vac shows -21 on the gauge under engine download, and like 19psi on idle. What could be the cause of this, i have yet to touch the wastegate, but i did replace the hose that goes to it.

 

Maybe one of the intercooler hoses are bad.
They might be sucking shut or have a hole in them.