Stalls after warmup(sometimes)

I have an 89 5.0. Up till recently it ran and idled great. It still idles great. My problem is, once it warms up, sometimes it will stall every time you take your foot off the gas. I can crank it right back up no problem as long as my foot is on the gas while cranking, and it will stall out again, OR I will rev it as it tries to stall, and it will idle at about 1500 RPM's for about 10 seconds and then stall all over again. If i start driving it's just fine, and the very next light i stop at, it will idle perfectly. Sometimes while driving my check engine light will flick on for a second and turn off, however, when it was hooked up to a scanner, it showed no error codes, I even ran it long enough for the light to flicker and it still gave no codes.

Any ideas?

Thanks,

Zak