Stalling after start?

One morning I went to start the car, and it started fine then right after the idle dropped down and then shut off. I started it again and the same thing. I then started it and played with the gas pedal, and I got it to stay running at a high RPM but once I let off the gas pedal it shut off. Now I would do this at a high RPM until the car was warm and shut it off wait a couple minutes start it up and would run fine. That lasted about 1 week then it stopped, and I didn't have any problems for about a month and now it is doing it again but this time I can't get it to run after I warm it up.