In closed loop operation the 02 sensors switch at the stoich point of the fuel and seeing as how most fuel nowadays is E10, the stoich point is 14.09 roughly which translates to Lambda 1.0. Most widebands are calibrated to give A/F based on the stoich point of pure gasoline, which is 14.64:1, so nowadays it behooves you to have a wideband that also outputs in Lambda, because no matter the fuel, lambda 1.0 is always stoich. Stoich is important because your stock 02 sensors will switch at it no matter the fuel used. The PCM when the car is started, goes into open loop cold start, once a number of parameter goals are met it then switches to closed loop running off the 02 sensors, but it also uses MAF data, so the MAF curve has to be correct. What I am saying is when the motor is at operating temp, the A/F for pure gasoline should be 14.64:1, for idle and part throttle. It will go to open loop (WOT) mode based on throttle position after a few short timers have timed out, then it will richen up to whatever is commanded in the base fuel table.
This all is contingent upon the MAF curve being correct. If it's idling at 11.5, once the engine is warm, the MAF calibration is hosed. It's way rich and you'll eventually get a CE light. This is something tuners see EVERY day with calibrated MAFs. Now if you are seeing cold start readings of 11.5, it probably still is off, but not by as much because some vehicles are richer in cold start depending on temperature.
Hope this helps!
This all is contingent upon the MAF curve being correct. If it's idling at 11.5, once the engine is warm, the MAF calibration is hosed. It's way rich and you'll eventually get a CE light. This is something tuners see EVERY day with calibrated MAFs. Now if you are seeing cold start readings of 11.5, it probably still is off, but not by as much because some vehicles are richer in cold start depending on temperature.
Hope this helps!