the Pierburg Boost Control Solenoid failure is common - I've replaced mine a couple of times - it's an easy fix so doesn't concern me too much - this last unit has been fine
another issue which could cause the same symptoms would be a stuck/seized Wastegate - this can be tested with a pump connected to the Vacuum Hose (it may be more difficult with Original Vac Hoses, I have Silicon) - remove the yellow hose (on the diagram) from the Boost Control Solenoid, connect a suitable Pump to the Hose and pressurise - the Wastegate Actuator should be seen moving behind the Exhaust Manifold.
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Paul.