I recently had a 4-1 header and fudo n1 style exaust and a K&N typhoon intake and an edelbrock 70 mm throttle body installed at a small shop in Killeen Texas (KR motorsports) and the "tech" said that with the new exhaust that I didn't need the second o2 sensor but the check eng light would stay on so he took the light out of the gauge cluster. My car is now running way worse than it did at stock meaning it stutters bad at start up and boggs at low speeds but runs like stock at higher speeds (50+). I know its not due to oil or any thing like general maint because I do that myself using nothing but mobil 1 synth. and K&N filters the plugs and wires are brand new and high performance so please if anyone might know what the problem is let me know