Big JohnB

Ok here goes!!! I have a Greddy Profec B spec 11 boost controller fitted to my 53reg STI. Under normal driving conditions its fine but if I gun it its telling me its overboosting but not dropping the boost level down as it should ( In low its set to 1.1bar in high 1.4bar but is going way past!!) If I turn the boost controller off the car runs fine and the display only goes upto about 0.6-0.9bar max. Any ideas what it could be? I've checked the hoses, oiled the solenoid but still its no better.
Any ideas would be much appriciated