Definitely inspect your wiring. Clean up your connectors (compressed air, inspect the pins) and put them back together with some dielectric grease. This one is going to be a bit more difficult to find because it is intermittent, unfortunately, but a couple things you can do.
Start the car, and gently pull on the wires and connectors (gently, because these cars are old AF now!) and see if you get get it to hiccup. If you can, then you can narrow down your search.
Look for signs of corrosion or damage to the wiring harness - especially rodent damage if the car is sitting around much. Take the time to clean up your grounds and make sure they are well seated and not corroded.
A couple other quick points...
Are your engine mounts in good shape? This is low on the list and somewhat unlikely, but I have seen in the past where cars that have really bad engine mounts are pulling on the wire harnesses and can cause issues. Replacing the mounts is unlikely to fix your current problem, but if you do have excessive movement then you may want to resolve that after you fix this issue.
As far as the PCM - I think it is highly unlikely at this time. It would be pretty unusual for a PCM to hiccup for such a short time period. If the car was warming up and the ignition signal was being completely lost with no sign of any wiring or connection issues, then I would be more suspect of it, but since it happens when cold and only momentarily I think that replacing it at this point would simply be a shot in the dark.