Identify This Hose Please
 

My first post, I've been reading and searching the forum for a while and thought I would jump in, so here goes.

I replaced most of the vacuum hoses and found this yellow hose. It's connected to a valve located at the back of the engine under the O2 sensor plug. I've attempted to identify it using Clark's and this forum but no luck. Maybe I'm missing something- hopefully you guys know what it is and where it should be connected. Thanks in advance.
http://forums.pelicanparts.com/uploa...1231250959.jpg