If you can get your hands on a scanner that reads live data...how long does it take for the engine computer to go into closed loop? We tend to forget that these beasts are controlled by stupid/lazy computers. They've gotta have everything delivered to them and they're not in the business of diagnosis. If the O2 sensor heater is not working, then the computer reaching "closed loop" status is never satisfied and the engine runs in a factory preset "stoiciometric fuel ratio" and that magical 14.7/1 air/fuel ratio is hit n miss at best.