Where does this go?

 My 1986 Cabriolet with DX engine has a tube running from the top connection of the Auxilliary air valve via a Tee piece to a length of rubber tube that's been plugged with a bolt. Anybody know where this tube should actually connect to? Picture attached.

www.cabby-info.com has pictures of the Vacuum Routing of the CIS.

http://www.cabby-info.com/images/Engine/84-87CISVacuum.png

looks like it could be for the injectors on the later dx engine with hydraulic lifter head, should connect to a plastic tube on back of the head. it may have had an earlier solid lifter engine fitted or head so may not have the connector for them