this started happening about 2 weeks ago so i went out and bought a scanner the code came out to P1273 (air to fuel ratio). I have the Injen CAI and helix test pipes with the simu. When i had the X02 exhaust on i never got the cel light then i went back to stock and about 2 days later i got the code? could this be that there is more back pressure and the O2 sensors are going crazy or is it because of the CAI which i got back in April?

 

Also i get this hissing noise when i let of the throttle say im at 7K rpms and it will hiss all the way down to about 1k. I changed every gasket on exhaust besides headers to test pipes. Every gasket was good but since i bought them already i figured i might as well change them. Im not sure if the hissing noise was there when i had the X02 on there because it was so loud you couldn't hear yourself think

 

Also i did search but no one has this problem. I forgot to mention the test pipes are non resonated which i think thats why i get that hissing noise. Unless someone could help me out and tell what kind of resistors i need and just get rid of the post cat O2 sensors