What it comes down to , is the airflow meter needs to be rescaled to suit the improved airflow or use of a aftermarket ECU and lose the MAF . It comes down to Volumetric Efficiency calculation. Factory Ecu uses the airflow meter in its VE calculation ,Injector flow , latency , engine capacity , fuel pressure , manifold pressure, type of fuel. When any of these parameters are modified they need to be rescaled.

Some cold air intakes change the airflow BEYOND the reading capabilities of the factory MAF making rescaling redundant. Power Fc compensates by allowing other MAF sensors to be fitted Nissan etc then rescaled. Some aftermarket ECUs allow this or ditch the MAF in VE calculation . The factory ECU is stuck with the factory MAF.

Volumetric Efficiency Tuning 101 .