Ok, not when i first noticed this but its definately apparant now, had regal phase 1 in feb, told me boost wasnt holding, prob actuator, so brought VXR one had thorney fit it and they told me boost was still worng and to change boost control valves. Brought 2, changed front one and it seemed fine so left it. Then 3 weeks ago i brought a regal precat and fitted it and as the car was on the ramps i changed the other boost solenoid. Now the car (under full acceleration) builds pressure then drops then builds again then drops and again so effectively kangarooing but over maybe 10seconds or so. What do you think is wrong?

Do i need to have the map adjusted to suit the precat? Or could the actuator be wrong?

I dont understand why its doing it all of a sudden.