Thanks for the replies but still confused!
Is the MAP unit the one on the front end of the fuel rail? If so, that is connected to a stub on the front end of the manifold. Immediately below this is another stub that is connected to the charcoal filter, so I have two connections to the manifold. The one I'm unsure about is at the rear end of the manifold, it may never have had anything connected to it but cI an't remember and surely it shouldn't be just an open to atmosphere?
Steve