easy fix for this it's called an anti-fouler... you can pick them up at your local auto parts store... DO NOT put this on your header put it on your s-pipe.
the general purpose for this part is to "trick" your o2 sensor that the stock air flow is still being used, the way this is done is the anti-fouler takes your o2 sensor a little back from the direct flow of air in your s-pipe this "tricks" the o2 sensor... CEL eliminated...BE CAREFUL when taking your o2 sensor out it is very sensitive....
here's a pick of the anti-fouler...
