My 2001 Expedition (5.4L, 2WD, 87K miles) sometimes won't start when warm. Cold starts are always fine. If I drive more than 5 or 10 minutes and have to park and turn it off, then I better plan on hanging out for a few hours. It cranks fine, but won't start. Sometimes it will fire up but the RPMs only get to 200 to 300 for a few seconds, then die. If I give it gas, it might see 500 RPM for a second or two, but won't help. It reminds me of 1970s cars sometimes dieseling (run-on) when you turn them off. My Expedition is well-serviced, usually drives well, never idles rough, never stalls, and never hesitates.
The dealer couldn't find the problem and whatever computer codes they checked were fine. I tried new air and fuel filters with no luck. Someone suggested that a sensor related to the idle air control valve (IAC) may be dirty, and putting the gas peddle to the floor with the ignition in the run position may help the computer reset its bearings (apparently an issue with high-mileage police Crown Vics), but that still didn't help.
Tomorrow I'll have Pep Boys clean the throttle body and the rest of the fuel system. If that doesn't help, I'll have to start testing sensors, but I don't know which ones are related. Someone mentioned O2 sensors, but I don't think the computer uses them at starting. Someone mentioned a vacuum leak, but that would probably affect idle and acceleration.
The symptoms are the same as this January 2009 post http://www.fordforums.com/f60/99-exp...-start-162771/
but no resolution was posted yet. It's also similar to this October 2004 post http://www.fordforums.com/f60/99-exp...t-start-87446/
Anyway, any ideas are welcomed (and maybe post to the January 2009 thread too).