Your pinout was incorrect for this version of ECUs :), and I had to spend quite a bit after getting obd2 installed from u, coz it turned out 5v reference signal for maf, tps and other sensors had been disconnected due to that wrong pinout.
Anyways, as per the ECU pinout diagram available with me, Maf's 4 pins are 12v, 5v, ground and maf output. I think the 5th pin is IAT, but I can't find which ecu pin to connect this 5th wire to.