'94 altima..stalling,rough idle,not starting

having problems with my '94 altima,auto-transmission.it idles rough,when i
give it gas its ok.sometimes for no reason,while driving fine,all the dash
lights come on and then completely stalls out.sometimes it starts up right
away,other times it takes up to an hour to get it going.any help would be
greatly appreciated.
thank you.