Out of interest, how's your water spray rigged up?
It is manual or auto?
If its auto, has a hobbs switch?
Where is the hobbs tee-ed from?

Disconnect the water spray, earth and power
Run without it for a few days
Potential here is maybe the water is getting to the AFM circuit. Long shot, but worth a try

Also, are you running a oil catch can?
Another long shot, but sometimes you can get oil in the intake to the turbo. And the oil usually in mist form, can potentially play havoc on the AFM. Again you might clean it and its back to the same problem again
I'd stick your finger in the silicon pipe and see if it has any oily residue