My car wont boost past 7 pounds

I have a 2004 A4 B6 manuel which I just purchased not to long ago. Its has and upgraded turbo from ATP, intercooler, upgraded diverter valve, and the ecm has been flashed by stp. My problem started 2 days ago. When I step on it hard the boost gauge when it reaches around 7 pounds of boost the engine beginnings to hesitate and the check engine light comes on. And then the check engine light flashes. If i let go of the gas and place the tranny in the next gear the check engine light goes back to solid. and the car stops hesitating. Not sure what the light is on for. however i did notice that I"ve been running on the rich side. So i went ahead and disconnected my MAF sensor and the car begins to operate properly however when i let go of the gas and the rpm goes back to around 800-1000 the car turns off. Any one have and advice????