Yep, the 2009 Avalon uses a wideband unit for the upstream sensor. So yes, it's as accurate as AEM aftermarket wideband unit.
Right now, I am using a bluetooth OBD2 adapter and a tablet with the Torque Pro app installed. To My understanding, the Torque app just shows the information as the car's ecu is interpreting it. At wide open throttle, according to the torque app, the afr bottoms out at 12.08 and sits there. Since, I've had the app, I've switched from a short ram to a cold air intake, went from single to dual exhaust, and installed headers. Still, I get the same 12.08 afr at wide open throttle. I was just wondering how accurate these numbers actually are.
With the introduction of wideband O2-sensor usage in OEM applications, ECU algorithms have changed to full-time closed-loop (using feedback). This actually makes it easier to hot-rod your car since ECU will detect the changes and adjust fuel & ignition. However, that assumes that stock programming is fully-optimised for power, most of time it's compromise of multiple variables such as emissions, durability & longevity with power-production being further down list of priorities.
ECU uses various input sensors
such as MAF, TPS, RPM, engine-coolant temp and air-temp sensors to arrive at initial injector pulse-width (duty-cycle). Then it uses the O2-sensor as feedback sensor
to make minor adjustments to keep AFR on target with desired values at that operating range. So... if pre-programmed target is 12.08:1 AFR under WOT @ 6000rpms, then ECU will adjust injector duty-cycle (STFT) to arrive at that same 12.08:1 ratio regardless of mods.
So... let's say all your mods resulted in an increase of +5% air-flow at 6000rpms, the extra air-flow would cause a leaner AFR the 1st time you run through WOT map. ECU will detect a leaner-than-desired mixture and re-adjust its STFT to +5% to re-hit its desired target of 12.08:1. Even though the AFR is same, you may actually have more air and more fuel than stock (and more power). So the figures you want to examine are STFT and LTFT values at those operating ranges to see if you indeed are making more power.
Similarly, those mods will result in less flow at lower-RPMs, up to say... 3000rpms. So again, look at your STFT and LTFT for WOT @ lower-RPMs and you may see a -5-10% reduction in fuel to match lower air-flow.
At WOT, 12.08:1 is a safe AFR and little rich for max-power, but still much better than the older Toyotas which was programmed around 10.5-11.0:1. Max-power on an NA engine typically occurs around 13.0-13.5:1, but you have to be spot-on most of time. Less leeway for intake-leaks or sub-standard gasoline than richer mixtures.