I have a 10/87 528e (born as an automatic) originally sold in California.
It is a little rubber nipple that plugs in under the throttle body, it connects to a big tube that eventually ends up at the charcoal canister. I think this circuit sucks fuel vapors out of the charcoal canister, but I don't know.
i can't find a part number on real oem...my part is all torn up.
