Vacuum system 1982

[FuzzyBob]

Vacuum system

Hi folks,
I have a 1982 250 L6 that I just rebuilt and I am chasing down a rough and surging idle..much of the advise here and elsewhere suggests checking the vacuums lines etc.. I have to admit the vacuum and emissions are not my strongest point understanding wise..and the vacuum diagram is only helpful to a point. So as I am going through inspecting and fixing I though I would post the questions and answers for all to enjoy..

So first question is what is this item circled in the picture and what does it do and should there be a hose attached to the port there?If so where should that attach? Its on the drivers side attached near the carb towards the back. It has one smaller hose going to the external air filter..

Thanks!