B2 air flow sensor - how much resistance is acceptable?

[David42U856]

Bosch K-Jetronic air flow sensor resistance - I've not found much on the internet on this subject but I'm sure there will be members who know the answer. I've just re-built the fuel metering unit for my 1985 B2 Audi 90 quattro and before I assemble it I would like to check that the air flow sensor is serviceable. The height of the flap is fine and it's concentric with the cone but I'm not sure if the resistance is acceptable. When I move the flap up and down the resistance is consistent but the it doesn't return to the closed position under its own weight. Should it? Does the fuel pressure in the metering head apply sufficient force on the control plunger to return the lever to the closed position? I'd rather not put it back together if there is a problem. The various manuals I've looked at don't really help.