I want to know if my tune will be affected if i adjust the fpr because my car idles at 12.3-13.3 afr and the pressure reads 45psi. Its fouling my spark plugs every 5k miles but i dont want to mess with it if it affects the tune. Engine is a d16z6, walbro 255, dsm 560cc injectors, stock fuel rail and stock fpr. I know some will say if its tune, leave it, but i bought the car already tuned so idk what the guy changed that might of affected it but will turning the fuel pressure down to stock at 37psi help move the afr to 14.7 at idle or at least close without messing with the tune? Thanks

 

Of course it effects the tune, its the fuel pressure. Changing the pressure up or down is like an overall fuel trim. Find a tuner to clean up the idle region of the fuel table shouldn't cost too much.

 

^ this.

And I wouldn't worry about if too much at 13:1.