I installed a comptech exhaust header a few weeks ago, and I've noticed that the low idle (fully warmed up) is rougher than before; nothing major, but noticeable.

I re-torqued all of the bolts between the header and the head and the catalytic converter; no leaks that I can discern.

I don't think I did anything that would have damaged the oxygen sensor, but I'm guessing this is the most likely issue.

Has anybody replaced their oxygen sensor yet? Any noticeable improvements? Bosch? Best price?

(By the way, other than this issue, I'm very pleased with the header itself! Excellent quality, and the car is noticeably stronger above 5k.)

 

As noted on another thread, I replaced my stock spark plugs (which had 12,994 miles on them) with Denso IK20s. The plugs make the car run noticeably smoother, and they seem to have solved the idle problem. I have less than 100 miles on the new plugs, but so far so good.