Rb25Det Neo Issues With Maf/fuelling

[Big Mac]

Firstly, greetings from the UK

I'm having a spot of bother with the Stagea, perhaps a few of you knowledgeable bods will be able to solve this little puzzle...

This is on an RB25DET NEO.

The MAF/AFM voltage (both at the MAF itself and at the ECU) is reading ~2.2v at idle, which is causing the engine to overfuel and preventing it from running/revving. If I unplug the MAF the engine pulls back the fuelling and idles fine, and will rev to about 2.5k at which point it pulls timing as it is in safe mode.
If I then check the MAF signal without it being connected to the ECU, it reads ~1.2v at idle, which is the correct value I believe.
So far I have replaced (all with known working parts):

MAF
ECU
CAS
I have replaced the wiring between the MAF and the ECU, and also run a new +12v live wire straight to the battery. Using a multimeter I have confirmed that the live and earth are good at the MAF, and also that the voltage on the signal pin at the MAF matches what the ECU is seeing.
I checked the Fuel Pressure Regulator to make sure tha thte diaphragm was OK, and it isn't chucking fuel down the vacuum line into the plenum (but then if this was the case it would still do it with the MAF unplugged I guess).
Injector time is around 2ms without the MAF connected, as soon as it is plugged back in this goes up to ~11ms (hence the overfuelling).

I'm now out of ideas as to how I can get this thing working again - can anyone think of what might be causing the signal to be incorrect from the MAF when it is linked to the ECU? Thanks in advance, this is doing my head in now.......