I recently bought a 03 WRX, 89k on it, had a Perrin Intake, Invidia (Catless) Downpipe, Cobb CBE, and what appeared to be an eBay header on it considering it had a nice crack in one of the welds. I got a decent deal on the car knowing it needed some work. I knew it was throwing the P0171 code, and assumed it was because of the exhaust leak about 3-4" from the O2 Sensor. Last week I replaced the header w/ a Tomei UE, and am currently running Cobb's OTS Stage 2 91 map (actually running 93 octane in the car, but I figured the 91 map would run a little more rich). After replacing the header I reset the ECU and the code came back after about 20 miles. I've since checked all vacuum lines, bench tested the front O2 sensor, and cleaned the injectors. I reset the ECU once more and the code stayed away for 3 days, but now it's back. A/F ratio at WOT is showing anywhere from 12.1-12.4 @ WOT (I know the factory O2s isn't very accurate below 12.5), between 14.3 and 14.9 when cruising, and as high as 24 when engine braking. My question is should I be looking more for faults with the car or could this simply be a result of the map I'm currently running?
All help is greatly appreciated, I've searched the forum pretty hard, but it seems everything to do with the P0171 is about fixing issues with the car. As I haven't found anything out of the ordinary, I'm starting to think that it may just be the tune.