Yet again this is a case of someone plugging in a scantool, reading a fault code relating to a mass air flow sensor and immediately assuming the sensor itself must be the problem. Please tell us how you've arrived at this conclusion? The scantool is telling you in the form of a fault code that the fault is being reported from the MAF, whatever the cause may be. It is not telling you the MAF is faulty, even though it could be. You are more likely to have a fault with air flow which means the MAF is reading accurately. The ECM is not capable of distinguishing the difference. It is a computer. It cannot think, or apply logic or reason. It does EXACTLY what its told. No more, no less.

IAT. Intake Air Temperature. It's located inside the body of the MAF. Since you now have a fault code relating to that ever since you changed the MAF I'd suspect you have the wrong part. The terminal pin configuration may be different and the ECM may not be able to read the IAT.

The code would've been generated when he disconnected the MAF and ran the engine with it unplugged. In this situation the ECM cannot read air flow at all, hence a code relating to Mass Air Flow sensor open circuit.

Prior to that the engine may have suffered a loss of performance, and that could be a MAF fault. However the ECM would not recognise a fault unless the return signal from the MAF fell outside of the ECM parameters. This is highly unlikely. The ECM would not be able to tell the difference between a faulty MAF producing a low signal from a healthy MAF producing a low signal due to the car being driven lightly. The ECM does not know you have a caravan on the back. It merely reads the volume of air passing through the sensor and acts on the signal received.

When you unplug the MAF the engine then performed as it should. This is because the ECM cannot read air flow and so it uses a pre-programmed subsitute fixed value instead. The MIL is illuminated warning the driver there's a fault with the system.