whats wrong when im on bypass water gage drops from 200 to 100 on 2000 Pontiac Bonneville

turbo charge gage goes from -10 to +10 and car keeps acting like its trying to sputter out or flood out or something i cant under stand what to do can some one help i just got the car used i dont have money to put out on car

Asked by for the 2000 Pontiac Bonneville