Whst would cause 01 grand am 2.4 motor to all of a sudden start sputtering and missing but only when the car gets to normal temp.when its cold it runs like a top

coincidence, we have a 2001 2.4l . I would start with the air filter,make sure nothing is living in it, change if needed. $10 , if not move onto the throttle body, have to take off air filter and hose leading up to it ,careful not to break sensor on hose, take cover off to expose throttle body, two bolts and there should be 1 screw to a clamp thru a access hole in cover. get that off and there's the throttle body. buy throttle body cleaner and a clean rag and spray and clean the crud out...it will need it. then onto the iac sensor (idle air control) $125 .should be good after that,if not go to spark plugs n wires,and clean packs. $20 wires,$ 5 x4 spark plugs. hope that helps.

Oit turned out the coil pack must have went bad at that time I Replaced it and it solved the prob