Peppers,
First of all congrats on the headers and welcome to the FI family.
I too had issues but not because of the headers but only because of installer ignornace.
I kept throwing a misfire code and a cataletic code which in return meant the 02 sensors.
Many cleared codes later and lots of trouble shooting. Come to find out. The damn shop put the 02 sensors in the wrong place. The primary was put inside of the J bend and the post cat was put inside of the header where the primary should of went.
BTW check your MAFs also on the intakes. Mine were dirty.
Hope this helps and FYI Tony has the best customer service hands down
