Rough running engine when warm

I have a Chevy P30 (basically an old bread van) which started running very rough yesterday on my way home. Out of curiousity I ran it again this morning and it ran fine until it warmed up. What would cause this? I suspect there is a simple solution, like a broken vacuum line etc, but if anyone has a clear idea I would appreciate any info…Thanks

In general any basic maintenance items could be involved - spark plugs, wires, filters.

Other than that, for a warm only problem I would first check the coolant temperature sensor.

What year is it?

Thanks for the suggestions. I’ll check plugs, wires filters etc…It is a 1995. This was not a gradual shift…It went from running fine to very rough basically instantly.

Check the coolant temp sensor - if the computer doesn’t register the van getting to full operating temperature it will continue to feed it a rich mixture - sort of like leaving the choke on after an engine is warmed up.