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?

1 answer
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: http://repairpal.com/OBD-Code-P0300