I think you have the wrong idea of how the ECU is achitected. Think about it as if there was only one map, and the sensors that tell it where to be are reading wrong. Those sensors in order of decreasing importance are CAS, MAF, coolant temp, O2, TPS. Your problem sounds like a loose/dying MAFS.

The Nissan ECUs of the SR20 era are pretty good, from what I understand. You just have to tell them the correct information.