Well, Tom, like me, you are experiencing what a sudden extended cold
spell can do to our vans. I'd think a wiring issue could be at the root
of your problems (with widely changing temperatures metal..and wires,
can change dimensions.) Something that was connecting before could
suddenly not be connecting..coupled with frozen water you could have
intermittant problems. Of course once the van has been running for a
while the problems should probably go away.

Pull (gently) a few wires. Check the area around your oxygen sensor and
see if it is excessively dirty (ice or salt covered). Look at your
engine in the dark and see if you notice any sparking (which you
shouldn't).