rpms erredic when warm on 1996 Mercury Villager

my villager runs fine when cold. when it warms up the rpms jumps up and down and i pulled over i saw the catalytic converter was red hot and it was running rough what can the problem be?

Asked by for the 1996 Mercury Villager
Sounds like the engine is misfiring. Get the diagnostic trouble codes to find out what is triggering the misfire.
Read this for info on what can cause this: