i just put on a performance aftermarket exhaust header on my 2002 honda civic lx 2door, 4 cylinder to replace the manifold and catalytic convertor. when i put the exhaust header on i only put on ONE oxygen sensor and it was the upper one(before the manifold). Now my check engine light is on and my idle is a little high, i was just wondering if maybe i should put the other oxygen sensor the lower(after manifold) one on and that would fix the problem or do i need a tune up on my car to reprogram the computer. Or is there something else that i need to do that i have not figured out please help.