well I've discovered even more wizzardy stuff. Inside the MAF is a multi turn trim pot, this allow the voltage across the hot wire to be calibrated for cats/no cats.

[Linked Image]

Oh and yes I've fitted a new Lucas Ignition amplifier (but its probably junk Lucas)

touching wood everything has been fine since I installed the resistor mentioned above.

2012 Plus 4 in Sport Green. Much comfier than the Plus 8!