Explorer won't start-intermittently

1997 Explorer V6, 117,000 mi. Every few days or weeks, the engine won’t start. The battery turns it over fine. Sometimes, the engine will not fire, sometimes it will-but sounds like fuel starved or firing on one or two cylinders. Let it sit for 1/2 hr. or more and it will start as if nothing wrong. It has never stopped while driving. Dealership worked on it for 3 days and replaced ‘crank sensor’. The fuel filter has just been replaced also. Now, it is doing the same thing and they don’t know what to do.

Any ideas?

Next time, press the gas pedal down about an inch and try to start it. If that works, it may be the idle air bypass valve (also referred to as IAC).

Thanks, I will try this method.