Update on boost control problem

Ok so the last 2 weeks iv been trying to get to the bottom of it, some times it will boost up to 0.7bar wich is wot it is ment to be and out of nowhere it will drop to 0.5bar and go no higher. You can start the car and when you rev the engine you can feel the boost control solenoid clicking and other times you start it it won't there r no fault codes on the ecu. if anyone can help that would be great