A MBC, morons boost control, is a bad idea. It disturbs the system so much that the Trionic ECU is unable to properly control and protect the engine.
This is the Trionic systems last attempt to protect the engine. It shuts of fuel delivery by closing the fuel injectors and shutting off the fuel pump. Before this brutal step the ECU tried to lower the boost, but the pressure leak caused by the MBC prevented if from opening the waste gate.
Saabs with Trionic systems should be tuned by software changes, not by introducing leaks that disturbs the control algorithms in the Trionic ECU. If you need more boost you have to get new software for the Trionic ECU and perhaps some new hardware like larger fuel injectors (you can't get more power just by adding more air), turbo, exhaust system, etc.