Pulsing on startup

1985 MM 2.6L 5 Spd, all stock. I've got what might be an unusual issue. When I start the truck up in the morning (usually cold out) it will fire up and then start pulsing until it gets warm. What's unusual is sometimes I can hear it run fine for one second after it starts and then it does the pulsing until it's warm. In the afternoon, I don't usually have the same issue. Am I incorrect in thinking there's a temperature sensor somewhere that could be contributing to this? Or is it perhaps a sticky choke? I believe I'm selling this one soon and I'd like to get it all fixed up.

How frequent is the pulsing?

Pretty quick, about every second.

You might have a vacuum issue somewhere, or the mixture screw is out of adjustment or a partially blocked jet. Take the air cleaner off and give it a blast of carb cleaner, start it up and try purging it. Start the engine and use your hand to starve the engine of air by covering the throats of the carb and revving the engine. Don't use a rag or something that'll obviously end up disappearing into the engine. I don't think there's a temp sensor that would affect idle (if there was one, it would either work or not). What is the idle rpm cold like? I'm kinda clutching at ideas here.