1998 Pontiac Grand Prix car just stalls

i recently had my car stall on me while driving. when u would try to start it, it would turn over then die. I replaced the mass air flow sensor, throttle position sensor and idle control sensor. the car worked fine for about a week but has begun to do the same thing again. sometimes it will turn right over and stay running but other times u have to wait a few minutes before it will stay running. sometimes it will run fine after that other times it will only make it a few blocks. not sure what else to change or what else to check. in order to get it to stay on sometimes u have to keep your foot on the gas