boost going to the actuator opens the wastegate, if you have a split hose or the hose has fallen off this will give you this problem. also the boost solonoid if its jammed shut, a simple test would be to put a piece of vacume hose from the turbo compressor housing directly to the waste gate actuator, this should give you 5 psi or so. if your car still over boosts with the hose directly to the wastegate its safe to assume your wastegate is jammed or actuator is stuffed.