Please note that if standard, the '84 uses digijet injection system, not
digifant, thus it does not have an AFM.
I had problems with mine but it turned out to be bad wiring in the loom for
the power going to the aux. air valve, connected inside the loom to the
injector hot wires.
This is very hard to trouble shoot because the connectors cant be found
without tearing into the loom
Not sure what your problem is but I would include disconnecting the aux air
valve to prevent the injectors from being shorted to ground.         Mine
would do that when the heating element became hot.
I never found this valve on the schematics or in the books but my '84 has it
and I recognise it from other VW fuel systems.
I rewired mine so that it cant happen anymore.
I would also clean all connections to the ECU, fuel pump relay and associated
wiring .Good Luck!
Steve Cotsford