I assume A3 8L, If your in the front of the engine bay with the battery on your right..follow the leads off the battery carefully and you find a big rubber gromitt of sorts ,as you come to the bulk head, you can slip a vacum hose down by the side of the wires in this grommit. it wont pinch the hose ..you may have to pull a very small corner of the heat shield carpet back a bit if i remember correctly....
The other option would be to look around the pollen filter.
hope that helps