engine will turn and start, but will then immediately die out. usually happens right after putting gas in it.

the engine will turn/crank & start, but will then immediately die out.  it doesn't do it all the time though.  sometimes it will start & idle normally.  it will usually happen just after I gas it, or when I leave the first place I stopped at, right after I have just gassed it.  most of the time it will start normally after like 15-20 tries at starting it.  or if I just wait for like 5-10 minutes to try starting it again.  although, after trying both methods for 2 hours yesterday, I gave up, and had to have it towed home.  the next morning I went to try starting it, and it starting normally on the very first try.