My 1991 940 turbo 160,000 miles (built June 1990 Mitsubishi turbo) has had the boost coming on almost uncontollably in the last couple of weeks. On gentle to somewhat moderate acceleration, the car seems fine, the turbo acts normally. Put your foot to the floor for a fast start and the car lugs REALLY slowly to 3000 RPM. Then the turbo kicks in and the boost gauge goes all the way to max (never done that in 9 years). Acceleration is amazing but the engine starts knocking like crazy. At highway speeds it just takes off but again knocks like crazy. The folks at IPD suggested I look at the vacuum hose to the waste gate. It's old but fine. I disconnected it from the intake and put vacuum to it (gently) and the waste gate valve moves and holds pressure. I have never changed any sensors, including the Oxygen sensor. Hope this is nothing with the turbo. Any help would be greatly appreciated.