I have a '99 F-150. Few weeks ago it would not start. I then turned the key to the ON position, heard a buzzing sound under the hood for a few seconds. When the sound stopped the truck would start. The sound was coming from the IAC valve. So I replaced it. Everything was fine for about a week. Then the problem is back. The ON position trick worked again, ( very slight sound from the IAC valve) Any suggestions. Do I have a bad valve or is there something else causing the problem.

 

when you say wont start is it cranking?? or nothing happens?

 

What happens is when I try to start the engine it cranks over and seems to want to fire up but won't. I then turn the key to off, then to the ON position wait a few seconds. I here the IAC valve activate (slight hum) when the humming stops, I then crank the engine and it starts right up and runs fine. This is a new valve I just put in. The old one buzzed much louder, so I replaced it and everything was fine for about a week. Then the problem came back. I don't know if the new valve is faulty or something else is causing the problem.

 

you are probably hearing the fuel pump prime thats the humming. i.a.c valve doesnt make noise like that.