Isuzu Repair: What r the signs of a burnt valve, vacuum leaks, vacuum leak

Question
My grandmother has a Rodeo.I think it's a V6.It has a rough idle.What are the signs of a Burnt exhaust valve.Any noise,side effects.

Answer
a burnt valve would mean unburned gas, your o2 sensors and catylitic converter would be ruined and other things. your rough idle is moslty due to bad intake gaskets causing a vacuum leak, or a vacuum hose is leaking or bad, vacuum leaks causes rough idling check this first ok?