Paul,
check if you have the ROW setup (seems so, b/c you have the tee joint) as shown in
http://www.pelicanparts.com/911/911_Parts/1978-83/1-7-2.JPG
The missing connection should go to the vacuum switch (part #17A, sometimes called thermo valve) and from there to the WUR. If the line to the WUR doesn't carry vacuum, the hot engine idles too rich and may surge. I guess the US setup for a 1981SC should look like
http://www.pelicanparts.com/911/911_Parts/1978-83/1-7-3.JPG
but I don't see a tee joint there.
BTW, if you have a vacuum switch, then it is located near the WUR and has the part number 911 606 106 0X.
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Robert / 80 Targa
[This message has been edited by robs (edited 08-17-2001).]