1989 Ford Mustang car sputters and acts like it has no powe

1989 Ford Mustang 4 cyl Two Wheel Drive Manual

Ok, here is the problem. I bought the car and it had a 2.3 turbo motor swapped into it. Well when everu get on the pedal it will boost to 5psi and then start sputtering and u here the boost exiting out of the exhaust and u have no power at all after 3-4000rpms. We chk'd the timing replaced the plugs wires. Ive read that these cars should be running 15psi easy all day long and still get decent gas milage I get crappy milage and it feels liek my car has maybe 50hp