Idle Problems??? -> The Solution!

[rwinch]

I had to perform my first "real" repair on the Expy, which at 97500 miles is not a bad run.

The Problem: the engine immediately stalling out after it started. It just would not keep running unless you kept the gas on.

Now there have been several posts on this board (thanks monsta et al) and others about this and similar problems, but only a couple named the needed part, so I started this thread with an obvious message header so that all hopefully will read it.

The Solution: change the Idle Air Control Valve (motor).

Changing this immediately solved my problem.

From some of the other Idle problems I ran across, I would think it is a good bet that replacing the IAC valve would help out as well, such as:
- Rough Idle
- inconsistant or varying Idle
- the occasional "hiccup"

For those of you that do not know what this thing does, it varies the amount of "extra" air into the intake system to maintain a smooth idle, and help with emmisions. It does this by taking a pulsed signal from the computer, which is monitoring several sensors.
So it basically moves its little valve back and forth according to the pulses it recieves from the computer. Now if the valve gets sticky, or for some reason it can't respond quickly to the pulses, the idle suffers. So it would seem that quite a number of idle problems can be caused by this valve not working.
At least it is a start!

I got the OEM part from Ford, and they are picky about getting the right info on the truck, because the emmisions systems were "calibrated" at the factory for specific model runs. The part counter guys told me there were 15 IAC's to choose from. I was skeptical, because you could order a single part from Advanced Auto, but maybe here is a case where the OEM part is better. So anyway, if you are getting the IAC from Ford, be prepared to give the parts guy (or gal), the following info:

- Model Year
- Engine Type

Then EITHER the:

1) VIN (yes they can tell the above with this)
or
2) The calibration code for the Expy which is found on the DOOR JAM (not the door with the tire pressure sticker, but on the door fram itself).

Apparently, the calibration code was stored by Ford as a function of the production number of the VIN, and they can go online to see what it is.

Anyway, the Expy now runs SMOOTH.

Now, replacing this little bugger is a trick because it is located WAY back under the cowling on the rear side of the throttle body. When you pick up the IAC (and the new gasket), get a couple of new bolts, because when you drop them (like I did) while trying to snake them out with two alcohol shaky finger tips, you will NEVER SEE THEM AGAIN!!!

Good luck and if you need the description on replacing the IAC, email me and I will send it to you.

 

[PaulC]

I'm assuming that rwinch has a 5.4 engine in his Expy, given his description of the accessibility of the IAC. The 4.6 engine locates the IAC on the driver's side of the throttle body and in a more forward location, away from the cowl.

Changeout of an IAC on an Expy 4.6 is about a ten-minute job, including the time necessary to remove the plastic "4.6" cover over the throttle body.

If you do this job on either engine, pull the negative battery cable off first, and leave it off long enough to provoke the engine management control system into it's learning mode, as the IAC and the control system need to become acquainted with one another. You'll know you've left the cable off long enough if the guages in the instrument cluster show the needles sweeping across their faces just after the first start-up.

 

[bnvus]

Couldn't agree more. You don't want to mess around with something as important as emissions. The IAC does exactly what RWinch has described. In essence it is a REALLY smart choke because of the computer.

To elaborate on what PaulC says. When ever the battery cable is pulled you erase the fuel trim codes the computer stores. They are a history file of how the engine has been run and provides the Engine management system an average air fuel mixture based on the stored codes. This is part of the reason that when you disconnect the battery the engine will run like crap until it learns the new trim codes. Just some Techy info for some of us who wonder how it works...

 

[PartTimer]

Wow, my truck just starting idling terribly when started cold. Even after warming the RPM's still bounced a little. How much is this part?

 

[rwinch]

If I remember, it was somewhere between $50-$70.