90 100q Odd stalling problem

[SJ]

Last week I was shoveling snow to dig out the cars. I started up the 90 100q
to get it warmed up and continued shoveling snow. After about 10 minutes, I
noticed the engine was not running. Tried to start it . . .nada. It cranks,
but no start. At the end of each cranking session, it sounds like it tries
to catch. I went back to shoveling.
A couple hours later, I tried starting it . . .. Vroooooom!    Worked like a
charm. Been working fine for a week.

About 2 years ago, it did the same thing. Wife started it up in the morning
and drove off in a few minutes. It stalled about a mile down the road. The
engine cranked but would not start. I had to tow it home. Next day, it
started right up! Its been running fine until that one incident last week.

The only common thing during the two events was that it was cold.

After the first incident, I took apart all the grounds and cleaned them. I
also cleaned as many connections that I could get to.

The cat and oxygen sensor have been replaced since the first incident.

Anyone have any ideas?  Intermittant idle switch?

SJ
85 Dodge PU, D-250, 318, auto
85 4k - - sold but still on the road
88 5kq
90 100q