Wastegate Valve Suction Test
WARNING: This page is about a different car, the 1996 Volvo 850. However, it is still accessible from the selected car via links, so may be relevant.
Disconnect vacuum hose from pressure regulator. Attach hand vacuum pump to fitting. Increase vacuum slightly. Look through holes in flange to see if wastegate valve opens. Wastegate valve should be fully open at 6.5 in. Hg of vacuum. Replace as necessary.