the front hole is for the fresh air. but since you likely have a TB adaptor plate, it may not be plumbed at the fresh metered air passage to the TB flange.

gen5 guys can easily run a hose from post maf/pre tb to the OEM fresh air nipple....that gen3's don't have (but you can add)

btw please tell me you pressure tested the core? a lot of em cracked n developed leaks