Sounds like a wiring short from the AFM to the ECU.

As an example, at the moment my AFM is fucked and the car is running around in limp mode with the AFM socket disconnected from the intakke pipe. Now last week in Perth driving in very very heavy rain the car just completely died on the freeway at 5am.

Solution was to physically blow the water/moisture out of the AFM socket that was causing the electrical short circuit. Car ran fine after that - all be it still in limp mode.

Has the workshop checked the AFM wiring back to the ECU with a multimeter ?

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