On my '87, the short hose between the idle stabilizer valve and the air chamber below it has a molded fitting that looks like a hard plastic vacuum line should connect to it.  I don't see this in the Bently.

Should this hook up to something, or did someone replace the hose with the wrong one?

(Yes, it's really a vacuum connection. Plugging it makes the engine idle MUCH better.)

This could explain why someone set the idle mixture to full rich.

Ah, the joys of working on a vanagon that has been butchered by someone who had no idea what they were doing. (Repair shop name available by request)

Bill