hi tangles
ive checked the VH41 / Q45 AFM ramp in the RB25DET powerfc and its not that much different to the Z32
the Q45 has a touch higher airflow values in the higher range, sub 3v but below that it's pretty close
i would expect your car to idle with Q45 AFM's even if you can't select them, if anything it should be a bit grumpy and maybe blow a bit of smoke at the worst case. with my R33 GTST and stock AFM (s2 AFM) im able to choose VH41 / Q45 from my AFM menu while the engine is runing and it keeps idling, the idle drops a note but it continues to run correctly (i would expect it to).
so i expect that something else is wrong, mangled wiring, incorect wiring, dead AFM etc
you could check them both out at ETC, SENSOR SW CHECK and look at AF-1 and AF-2
they should be pretty close at key ON (but not start) and shouldnt have a black highlighted background on the sensor name