Originally Posted by xluben
The stock O2 sensor is a narrow band. It works fine near stoichiometric AFR's (closed loop), but is basically useless for open loop.
Who tuned you and how did they tune your car without a wideband O2 sensor? It seems like FIRST thing you should have done after correcting a major leak is get retuned.
It was tuned by Eric at Torqued Performance with his wideband. I had been using the stock 02 to monitor trims. The car was on this tune for 10k miles without issue. Fuel trims were always +/- 7% until one day about a month ago when I caught them creeping up on a highway cruise. Problem has persisted ever since.
I assumed that because the leak was not there prior to my first tune that I wouldn't need a retune. Ditto for swapping out TMICs. I reset the ECU and also reflashed the map.