Disconnect IAC and truck runs GREAT!

rgoers · September 1, 2006

Truck is a 2000 Explorer Sport, with 4.0 SOHC.

I have a MIL on, and a P1506 code. I searched the forum, and all I can seem to find are stalling issues related to the IAC and P1506 codes. Seems like the 'norm' is engine stalls flat out if you disconnect the IAC electrical connector.

Mine seems to be the opposite. When I start it, it revs high, and stays high for several seconds. If I give it gas (by hand, at the throttle body) it does the same. Revs high and stays high before settling down. If I unplug the IAC, it revs and settles immediately. It starts and idles smooth with the IAC unplugged. Seems like I have a LOT more power as well. I have driven it 2 days like that so far. Runs like a champ (except for the MIL light still on, this time shows IAC error along with P1506... wonder why?

)

Anyway, I bought the truck used, about a year ago. I've felt transmission problems every time I slow down to stop, since I bought it. That issue has GONE with the IAC disconnected. Perhaps it was messed from the day I bought it? Seems like it returned to idle WAY too slow, and though I was braking, the engine was still trying to run away.

Anybody ever hear of an IAC failing in this manner??? I ran through the service procedure, and the IAC measured 26 ohms. The spec is 6-13. I have a replcement IAC on order.

slpdave · September 1, 2006

Nope...only heard of rough idles and hard starts when cold.

David

dogfriend · September 2, 2006

What's your idle speed with the IAC disconnected? It should be kinda low, less than the 750 - 830 rpm that is normal (warm engine, trans in P or N).

If its higher than that, I would look for a vacuum leak that is letting in extra unmetered air.

rgoers · September 2, 2006

dogfriend said:
What's your idle speed with the IAC disconnected? It should be kinda low, less than the 750 - 830 rpm that is normal (warm engine, trans in P or N).

If its higher than that, I would look for a vacuum leak that is letting in extra unmetered air.

I pulled a freeze frame on it from my ODBII reader. Says it's idling at 820 with the IAC disconnected.

Funny thing is I have always had the high idle problem at startup, after tapping the gas, and when slowing down. I thought it was just characteristic of the truck.

I didn't get my first MIL error until right after I installed a K&N replacement filter (hoping to up my mileage a bit). I was thinking the P1506 was caused by the K&N, so I cleaned the MAF and went back to a Fram filter. When that didn't help, I started looking to the IAC. I have the same service reference as you included in your post. I used that to get me to the electrical checkout of the IAC, and I found the resistance to be 26 ohms, instead of the 6-13 ohm spec. That's why I ordered a new IAC.

dogfriend · September 2, 2006

My idle drops down quite a bit when I unplug the IAC. Check out this video where I demonstrate the IAC woooo.

http://homepage.mac.com/dogfriend/Explorer/iMovieTheater14.html

If your new IAC doesn't solve the issue, I would look for a vacuum leak.

rgoers · September 2, 2006

dogfriend said:
My idle drops down quite a bit when I unplug the IAC. Check out this video where I demonstrate the IAC woooo.

http://homepage.mac.com/dogfriend/Explorer/iMovieTheater14.html

If your new IAC doesn't solve the issue, I would look for a vacuum leak.

The movie didn't want to play for me. I'm on a WinXP machine, but I do have fully registered QuickTime Player. Still... no workie. What's the IAC wooooo? Is that the issue with them making a hooting sound?

Anyway, I get NO difference *at all* when I plug and unplug the IAC while the engine is running. None, zippo, zilch.

dogfriend · September 2, 2006

rgoers said:
The movie didn't want to play for me. I'm on a WinXP machine, but I do have fully registered QuickTime Player. Still... no workie. What's the IAC wooooo? Is that the issue with them making a hooting sound?

Anyway, I get NO difference *at all* when I plug and unplug the IAC while the engine is running. None, zippo, zilch.

Sorry the movie doesn't play - in the movie, I unplug the IAC and the idle speed drops about 100 rpm or a little more.

If yours doesn't change then your IAC isn't working right or you have a vacuum leak somewhere that is also letting air bypass the throttle plate.

The IAC is also sometimes known as the Idle Bypass-Air valve because that's how it functions - it allows a controlled amount of air to bypass the closed throttle plate to control the idle speed.

rgoers · September 3, 2006

Where should the plunger be normally (no power to it)? Mine sits open a little (maybe 1/16th inch) when I take it out and look at it. I'm assuming the rest position would be wide open, or closed, not "half-way open".

dogfriend · September 3, 2006

Not positive, but I think the opening is supposed to be proportional to the voltage in the PWM signal that is applied (i.e. supposed to be closed with no voltage, supposed to be wide open with full voltage, the opening is modulated by the time the PWM signal is on)

Anyway, I think this applies to your truck:

Runnin'OnEmpty · September 5, 2006

Since this is a used vehicle, it's possible that a previous owner bumped the curb idle up with the throttle stop screw. Maybe to compensate for a failing IAC...? Service manuals say you'll suffer a life of despair if you tinker with this screw, but if you must, it should be set so that the engine stalls after about 5 seconds with the IAC unplugged....

dogfriend · September 5, 2006

Runnin'OnEmpty said:
Service manuals say you'll suffer a life of despair if you tinker with this screw,

What if you're already suffering a life of despair because you bought a Ford? Will tinkering with the screw make everything ok again?

Runnin'OnEmpty · September 5, 2006

Ha ha, ROTFL Dogfriend. I don't know, it might; I'll have to try it.

Actually the Sport is running great right now, but I know things can change at any moment......

rgoers · September 5, 2006

HA!!! Good one. I normally buy *anything* NOT made in the USA, but thought I'd take a chance on a Ford after having such a good experience with my Nissan/Mercury Quest/Villager. I did next to nothing with that vehicle, and sold it with 247,000 miles, still running strong.

Actually, the Explorer was dirt cheap, and I needed a 4WD to pull my sled trailer...

It just so happened I was able to pick up a 5 year-old vehicle for 20% of it's original cost - so I went for it. It hasn't been too bad of a vehicle so far. Hey; I pulled a friends Tahoe out of their back yard. He buried it, testing out the 4WD that the dealer was *supposed* to have fixed! Guess not... Boy was he embarassed!

Anyway, the guy I bought it from didn't wrench at all, so I doubt he messed with it. My best guess is that the plunger is STUCK part way open, and that's why it doesn't die when I unplug the IAC. When I remove the IAC, I can see the plunger is not resting in a closed posiion. I'm guessing that it should be. I'll see when the new one comes.

gijoecam · September 5, 2006

Indeed, it sounds like the IAC froze in the closed (or almost closed) position, so someone tweaked the idle screw on the throttle body to compensate for it. That's really not the proper way to fix it, of course. It just masks the problem with the symptoms you described above.

There should be clearance behind the idle stop screw and the throttle linkage. Back it out and see what she does.

-Joe

rgoers · September 5, 2006

There's a good 1/8" between the plunger and to where the IAC "would" be fully closed. I can grab the shaft with a needle-nose pliers and push it closed, but it just pops back open again when I let go.

On the other hand, the throttle butterfly looks like it is closing completely. Not even a hint of light there... it's closed!

Anyway... before I unleash all the demons of hell by tinkering with "THE SCREW"

I'll see if the new IAC makes life perfect again. If not, *then* I'll have to try unleashing the demons...

budwich · September 5, 2006

I doubt that the pintel should ever be fully closed. With your throttle totally released, as you have found the butterfly is totally closed.... you won't get air from anywhere other than the IAC bypass. I have a "spare" unit and its the same a small opening. That's just my guess. Your ohm measurement doesn't sound right though.

rgoers · September 5, 2006

budwich said:
I doubt that the pintel should ever be fully closed. With your throttle totally released, as you have found the butterfly is totally closed.... you won't get air from anywhere other than the IAC bypass. I have a "spare" unit and its the same a small opening. That's just my guess. Your ohm measurement doesn't sound right though.

Buzzed it twice, with a good digital meter. Tried both polarities too, just in case there was a diode in there. Came out 26 ohms both times.

budwich · September 5, 2006

sorry by "not right", i meant ... not good as in not what is expected. not you didn't do it right.

rgoers · September 5, 2006

budwich said:
sorry by "not right", i meant ... not good as in not what is expected. not you didn't do it right.

Yeah, I knew what you meant. I was just repeating the measurement I got. I'm seriously *hoping* the unit is BAD!

Disconnect IAC and truck runs GREAT!

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