sometimes won't start on 2001 Ford Explorer

sometimes when I go to start it, i can hear a soft humming of what i think is the fuel pump and the engine starts fine, but sometimes i cant hear that noise, and it won't start. sometimes if i wait a min or two and try it again, maybe after a few tries, eventually it starts. what could be causing this?

Asked by for the 2001 Ford Explorer
does it start and stall immediately? if it does you have an idle air control valve problem.the humming noise is a telltale sign of it also.see it alot!!!