Originally Posted by BalanBro

When you are running in closed loop conditions (partial throttle, low engine speeds) where the car is getting feedback from the o2 sensor, the car will always be making adjustments for the given demands. I suppose in this scenario, it may seem like the car is learning since it is "adapting", but all it really is doing is trying to get close to 14.7 AFR to conform to the ideal stoichiometric fuel burning ratio.

Look closely at what Jesse is saying. It is subtly different. The car is not learning your driving habits. It is looking at whats going on in realtime and trying to figure out the answer to, "okay, now what do I need to do to get back to an optimum afr becase my O2 sensor is showing that I am currently injecting too much/little fuel."

Under WOT/high load (open loop) however, the car is going to disregard the o2/AFR sensors and base tuning off a predetermined map. The car will look at 1)engine rpm and 2) MAF output to obtain a load value, and basically use these values in a fuel table to look up the factory preprogrammed fuel injection duration, and a timing table to look up preprogrammed ignition timing. These maps are static and do not change, unless you were to go in and physically modify the tables.

Late 90's/early 2000 nissan OBDII ecu's had the tables stored in read only memory and could not be altered whatsoever. Aftermarket tuning solutions for these cars had to utilize daughterboards which house external roms that the end used could use to make their own map and "burn" to the rom. Once again, this data cannot be altered by the ECU itself.

Now I can't say I know what is going on for the latest nissan ecu's, but I think the only real difference is the type of memory used which allows for the data to be flashed by some of these aftermarket tuners.