Whats wrong???

Please someone help me with this one. I started my 95 prizm last night and it just sat and rumbled like the idle was way off. i put it in gear and push the gas and i couldnt get my revs up. Its like something is clogging up my catalytic converter or my valves are messed up. Someone give me an answer.

the same thing has happened to me twice. i changed out the alternator and everything is fine now