Well, I've run a bottle of injector cleaner and, on the next tank, a bottle of seafoam though it and nothing has changed.
It took a while to be sure, where it's a bit random in "when" or "how severe", but disconnecting the intake solenoid does not cure the missing problem. I have noticed that when it acts up it starts fine and then, very soon after, gets rougher as the temp needle makes it way through the blue area on the gauge. It smooths out about the time the needle clears the blue area.
I have not found time and weather condition to take on swapping injectors yet. Meanwhile, I'm open for other ideas.