My air/fuel gauge has been behaving poorly for quite some time; it will randomly read "full rich" (ie. it's reading a 1V signal) for extended periods of time, without any fluctuation. Suspecting a bad O2 sensor, I replaced it today with a Denso unit from Pro Street. Readings are now correct, although the sensor appears to need to "warm up" or initialize in some manner before it reads correctly; it will read 1V for a few minutes after starting the car, then do the usual "blink-blink" dance. Initial "seat of the pants" testing suggest that the car is pulling a little harder now, which is both surprising, and purely subjective.