Game's FPS is wonky ( read for better explanation)

So recently TS the FPS is wonky no I am not talking about lag spike. I'm not sure why this is happening to be honest but I have accidentally set my PC to only use 2 out of 4 processors but fixed it to use 4. ok now for the example route NEC NY to Philly before 190 FPS now 45-50 FPS. I have no idea why this is happening to me 
