The thing that tells the ECM to go into closed loop is an O2 sensor voltage starting to swing. That gives it something to work with and adjust timing and mixture. If it's doing this cold, and if the sensor is new, it's probably not that then, although try disconnecting it when running fine and see if it makes it run like problem times. One thing you didn't say that you checked was to see if the sensor heater was getting voltage. There is a relay that powers that, and without it, it extends the time to go into closed loop. It should be fine warm and in open loop though, but maybe you have something that contributes to it not running fine under preset mixtures... The timings you give are very similar to the timings of an O2 sensor with and without heater coming up.
Seeing as how you worked on the manifold, the egr, if a 92 has one, would be my next bet. If it's like the 89, you can play with the shaft. This would be a big bet. It might stick when cold. If it has one, then disconnect the vacuum line to the egr proper (not to a solenoid valve) while it's hot, at idle, and fine. Plug it. See if the next cold start runs any better. Fiddle with it. Something tells me the 92 doesn't have one though, and it's too cold and late to go check mine...
Next two would be to listen for a vacuum leak. If it makes it run rough, and not just raise the idle, it'll be big. The other is the throttle position sensor.
The key symptoms seem to be:
- happens at a little warm (unless the O2 was faulty, it's just gone into closed loop then)
- goes away with rising temp (it's near the block or manifold)
- can go away immediately with a restart (electrically driven or sticking vacuum driven part)
You said a restart can almost always make it go away. Instead, make a list of electrical components and their connectors, starting with relay type stuff. When it does it's thing warming up, quickly try disconnecting and reconnecting each. You may have a few weird other effects, but it might narrow down which thing is responding to having power cut then reapplied. Many items may cause it to run rougher when disconnected, but if it works great when you quickly connect it again, I'd dig further down that path...