Good point. In fact you can try something simpler if you have the discipline - route a vacuum line directly from the vacuum pump to the wastegate actuator. This will shut the wastegate flap when the engine is running. There will be no ability to regulate boost! If you go easy on the pedal as I imagine you do in the course of everyday driving, this will simulate the effect of cutting the ECU out of the equation.

Don't get me wrong, duxthe1 makes an excellent point. However, I've driven a 2.5 and I don't see any reason to apply more than half throttle in normal driving. The IP would never be under full load. Such being the case, I don't know how effective fixing bad microswitches can be at sorting your intermittent boost situation as I understand it. It's quite possible I don't have the facts straight.

Sixto
87 300D