UrQ Intake Manifold Question

[William Elliott <wcelliot@concentric.net>]

Okay, this is a stupid question, but I can't fnd the answer in any of my
references:

Today while driving down the interstate, a loud whistle began.  When I
pulled over to investigate, the car wouldn't idle. Since I've just
fitted my 3rd IC-IM hose, I assumed something else was wrong for a
change.

Front and center of the intake manifold (just above where the intake
hose attaches) is a raised flange with a threaded hole in it, causing a
significant vacuum leak. While I've never noticed this hole before, I
assume I'm missing something. ;-)

What specifically goes here?  If it's just a bolt plugging a test port,
anybody know the size and pitch?  Nothing I have here at home seems to
match.  (It appears to be 6mm, but neither fine nor coarse bolts seemed
to fit.)

Thanks!
Bill Elliott
Lake Mills, WI
85 UrQ whistling while it works....