My 07 997.1 C2S has x51 headers, AWE 2nd gen cats, and AWE mufflers.
I had CEL issue at first but fixed the problem with O2 sensor spacers.
No problems after that for several months. My car runs well.

However, I got an error code, P2196, yesterday (O2 sensor sig, Stuck Rich Bank 1, Sensor 1). I was doing HPDE2 at NJMP yesterday and all I did before I bring my car to the track was change brake pads, bleed brake fluids, and change engine oil. My car still runs well.

Anyone has an idea? I hope it is not a major issue.