This is gonna sound crazy,but I had an '84 SD that pulled oil up to the Ign.Sw.
and from there to the A.C. controller.
'cleaned everything up as best I could and replaced the vacuum shutoff on the
back side of the Injection Pump.(put a Primary/clear/V.W. fuel filter in the
line between the ign.sw. and the I.P. shutoff to give me some advanced
warning in the future.)

Vacumm is a wonnerful thing, BUT eventually everything ends up at the PUMP.

To answer your original question: The vacuum shutoff's default (without
vaccuum applied) [or a "BAD" shutoff] position is only waiting for the starter
to apply R.P.M.s after the Glow Cycle...COMPRESSION BASED IGNITION!