I needed to remove this vent as very time I had the fan setting on max and hit a speed of about 20mph the vent would slide to half open and restrict the air flow so much I could barely feel it.
To remove grip the outer edges with your fingers and pull the entire unit out one side at a time:
Vent removed
Gap left
Rear of vent
I found that removing the flap at the back and turning it around gave me the result I was looking for. Meaning that when open it wouldn't close any longer at full speed.
Al