[MotoSook]

That's the turbo air meter. The comments you read concerning the the screw are for NA cars on which air flow pushs the meter plate up. The turbos force air into the meter for the top..pushing it down.

Edit: movement of the air plate should translate to movement of the fuel distributor plunger. Fine adjustment of the plunger height changes your idle fuel quantity. Put the fuel distributor on there with the plunger (Be careful you don't drop the plunger on the floor and nick or scratch it) and you'll see what happens. Without system pressure applied to the fuel dist. you won't have much resistance to the air plate movement, but you'll see how it all works together.