Why don't EFI engines just monitor all the normal perameter they normally measure but then when it comes to actual fuel program used, it instead lookes at the a/f ratio and adjusts it accordinly. I know it does this to an extent in partial throttle mode, but say if you were to add a whole lot of parts or even have a clogged air filter, the A/F meter, which is at the very end of the combustion chain will be able to tell exactly what is going on and the computer can then adjust the fuel to either go leaner or richer. The ECU could just sample like 500 times per sec and keep the a/f just right or hopping back and forth like it normally does under partial throttle. It could then use this same technique under WOT to keep the car at a relatively good stoich to rich area, that would be tailored for individual car. The car could also continually learn the characteristics of the car, so that any change in the motor would be addressed on the fly.

Sorta like the Hondata 'Autotuning' mode.

 

You would need a wideband o2 sensor like the Hondata system uses. The stock o2 only works over a very narrow range.