It could be. I don't really know what it does. On another make of car there is a vacumn line that starts out from the airbox before the throttle (no MAF on this particular vehicle). Its purpose is to supply air to the EGR system. It has something to do with creating the vacumn, or possibly venting it.
1997 Probe "16V" SE
NGK Plugs, K&N filter, Eurospec 16V emblem, GT fogs, and hopefully more soon...