Every time I lay into the gas, RPM's come up like normal and turbo spools up and then it just falls on its face, shuddering and sometimes backfiring. All the sensors are ok and the timing is good. My machanic friend said to check the waste gate. It moves freely but when we checked it with the car running the thing was barely moving. And it doesn't pulse or studded like all the others cars I've seen. Any help will be greatly appreciated.