Alright so today I took the truck out to Barnes & Noble to find a book. On the way down there the truck had no issues, ran pretty damn sweet. The check engine light comes on and off randomly, but its been doing that for quite a while now. Anyway, I get down there, go in there for about a half hour and then come back out, get in the truck to drive away. Fire up, its fine. Then I put it in gear and the thing starts revving up without me putting my foot on the gas, now it starts doing this pretty badly and I had to hit the brakes for it not to go hauling *** out of control.

So I shut the thing off, madesure the pedal was clear of any obstructions or whatnot that could be causing it to be applyed and then fired the truck up again. Instantly it revved right up to like 3500 RPM or so and was slowly still climbing so I shut the engine off so it wouldnt damage it. I looked under the hood to check if there was anything visably wrong and everything seemed ok. The pedal seemed to work fine so I tried it again. The SAME THING happened. So then I wasnt gonna risk the dangerous situation accuring again so I had AAA come get me and drag the Flareside back home on the flatbed. One guy walking by did compliment how well the exhaust sounded when it revved up while I was trying to get it going again, Im like yeah too bad I cant drive it anywhere!

But anyway, we get it home, fire it up again...hmm runs fine all of a sudden of course. Checked all the throttle cables, lubed them all up, they all operate as smooth or as smother then they did when brand new! So its not that.

I dove into my repair manual, found an intresting device called the "Idle Air Control" which is bypass air valve that controls the amount of air that bypasses the main throttle body valve to control idle speed. I am wondering if this thing could be all goofed up causing that issue? If that is sticking open then I imagine that could cause the engine to rev up like that.

The flatbed driver sugguested the cruise control, I highly doubt that though. I havent used it in a while and that would have had the pedal moving too when it was reving up I can imagine.

Alright guys, I need to hear some thoughts on this one. You guys come up with solutions for everything, I have faith in ya! Thanks alot

 

mine did the same thing. I fiddled with the throttle cable and the cruise cable and thought it might be going in a bind. I lubed it and its never happened again.

 

First thing I would try is taking off the intake tubes and watching the throttle butterflies and see if they're opening up (or stuck open) or the air is getting in from somewhere else. Somewhere else could mean the IAC, but I've never heard of one failing like that before. First time for everything though.

Hard to imagine a vacuum leak that sudden and that severe.

 

I vote iac as the culprit
real easy to remove and check for carbon or dirt build up

 

I'd start by having someone pull the trouble codes from the computer. That will give some clues on where to start looking. It probably would'nt hurt to remove the IAC and check for any carbon that may cause the valve to stick.

 

Yeah, one of my buddys sugguested a vaccum leak. But that would have to be one hell of a massive vaccum leak to come on so severe so quickly. Im gonna pull the intake hose off tomorrow and check it out some more. I definatly dont want this happening again.

Hmm I havent heard of a IAC failing like that before either, maybe if I dont come up with something else, Ill check the IAC for the hell of it.

 

my truck has been doing that since i got it. Mine'll rev up and down for about 3 minutes when i first start her up cold. Then she goes down to normal idle speed and i can go. If i put her in gear before she quits revving i get crazy high rpms without even touching the gas. My mech told me IAC.

Josh

 

Oh so it sounds like I was actually on the right track with the IAC, Ill check it out for sure. Its really the only thing that makes sense now that I think about it. Ive had a similar condition to MrRogers since this winter, though it hasnt been as bad as today and usually it would go away once the truck is turned off and refired. The Idle has been pretty strange lately come to think about it, ok Im definatly checking it out tomorrow.

Any tips/things I should know before I dig into the IAC?

Thanks alot guys, Ill fill ya in how it goes.

 

IAC maybe... You always here about them failing to open enough but I recon it could be getting stuck open. You could try cleaning it.... its only a 15-20 min job at the most.

 

I'd get a fresh gasket before you take it off. I use spray type carb cleaner on mine. That may not be reccomended by Ford though.

 

I just used gas on mine, but carb cleaner works better let me know how it goes.

 

Well we are gonna check out the IAC assembly this weekend, the truck seems to be running fine now. I completely soaked the whole throttle cable system and worked the butterflys real good and now the throttle feels amazingly good. It almost feels like the 05 F350 we drove with an electronic throttle...maybe that was the issue all along. But Ive heard enough people say to check the IAC out and clean it up, hell even if it isnt that it seems like an easy enough job and it will probably improve performance a bit!

Everyone says the IAC gets carboned up, where is this carbon comming from? Whats it like blow back from the engine or somthing? Or some fuel that gets heated up and carbonizes before reaching the engine?

 

Exactly, carbon comes from the oil mist from the pcv valve and whatever fuel and blowby reversion that gets past the intake valve. Some of this "goop" builds up just behind the throttle plates and creates drivability and idle issues. While you're in there, it would'nt be a bad idea to gently wipe the throttle bores clean as well.

 

You say you "soaked the throttle system and worked the butterflys". what does that mean? I'm wondering if that'll help remedy my problem.

thanks,
Josh

 

Well I basically just drenched the entire throttle cable system, where the cables end and control the butterfly valves (the air intake control valves which are located in the upper intake underneath the black cover on top of the engine near the intake manifold). I opened and closed the butterfly by hand while spraying with WD-40 and then some fancy silicone lubricant after the WD ran out, and I also pulled back the covers on the cable itself exposing the metal cable and sprayed them up well. I basically went nuts on them and really soaked everything well with lube.

Then I just lubed the area with the throttle cable comes and meets the foot pedal as well as the pedal piviot point. I sprayed into the cable cover from that end as much as I could. It all resulted in a MUCH more free and smooth feeling throttle.