Ok
Well yes there is a haynes manual, but they are hard to find.
If it does not open fully then you can adjust it
On the side of the carb is a housing with a couple of coolant pipes going to it
On the side of this housing are three screws
Once loosened the choke flap can be adjusted, by rotating the housing.
The adjustment is only small.
First you must set the choke flap gap (3mm) as described by the Haynes.
Make sure the flap is free to move fully open, and isn't snagging in the carb
This spring heats up and opens the flap, is it ok? Not broke?
You can see the adjustment amount on the three "ears"
That fits over the arm that moves the flap
That looks like this when its all back together

AGG 2.0L 8V. (Golf GTi MkIII)