1999 Ford F150 stalling

My 1999 F150 is stalling when I let off the gas. It happened the first time right after a fill up while on vacation. I was coming down from the Pinnicle in Cumberland Gap, and the truck shut off. I was able to get it started after a while, but the check engine light has remained on. It also stalled when we came in to a traffic jam on the highway. I am now having troubles starting it and keeping it running. Any suggestions?

Well, there are a number of things that it could be, but it is most likely to be that your IAC (aka Idle Air Bypass Valve) is sticking closed. You can tap it with a wrench or a hammer to temporarily unstick it. You can take it off and clean it to get it to work for a few to several months. You can replace it with the new revision part. They changed it a few years back to make it much less likely to get stuck closed again.

Do you know about how much this repair costs? Also, is it something that can be picked up by the AutoZone scanner if I take it to them to get the check engine light checked?

A stuck IAC will not show any OBD II code. A few years back, the part was about $80. It’s pretty easy to replace it yourself.

If your check engine light is on, then you should get the codes read and post them here before investing in an IAC. It might be something else that’s wrong, or you may have a sticking IAC and some other problem.

I took my truck to AutoZone last night to have the code read. The scan stated a problem with the intermediate speed. The gentleman at AutoZone said is sounds like an IAC issue. He sold me some carb cleaner, and showed me where the IAC is. I took it home, took off the IAC and hammered on it a few times. I then blew it out, and soaked it in carb cleaner. The check engine light has went off. I hope it stays off. Do you know about how long cleaing it will last - on average? I appreciate your help.

For me, about six months, but your experience may vary.

I think I will drive it for a couple of weeks, and if this appears to have been the issue, I will go ahead and replace it. The part was only $47.99 at AutoZone, so that is not too bad.

Thanks again for your help.

The truck is stalling again…same issues. It ran good for a few days, and then after a longer drive (about an hour), we went to start it and it stalled. We can get it started, but then it shuts off. I took the IAC off again and cleaned it. It started right up and rand good for a little while, and then after turning it off for about a half hour, I tried to start it again, and it stalled. The check engine light has returned.
Does this still sound like the IAC?

Yes, it does. I would replace it. (This is not a 100% certainty to fix it, but at least 75%.)

Hi Jeff,

I had a very serious stalling problem with my 2004 F-150 and I finally solved it by simply cleaning the MAF sensor. This device is located in the air cleaner plenum before the throttle body. Mine was removed by unplugging its lead and taking out two Torx 15 screws. There are two hair thin wires in this sensor which can become contaminated very easily and if they are, your engine will not run for crap. It will hunt during idle, and will stall at stop lights and going down the road. At best it is annoying, at worst it can be down right dangerous. Becoming fed up with this, I finally took my truck to a ford dealer. They had my truck for a week and agreed I had a problem but could not find the cause. I finally found a post on this problem on the internet, did what the gentleman said and my problem went away immediately. You have to remove the sensor, and spray it with electronic parts cleaner, right in where those hair thin wires are. You cannot do it without removal, and you cannot use anything but electronic spray. I used CRC Brand and it worked great. The repair was very cheap, being just the cost of the cleaner, and I have heard horror stories of throttle body replacement etc etc that did not work. Try this first, you may be very pleasantly surprised like I was.