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Old 10-24-2005, 10:01   #1 (permalink)
Henry Kolesnik
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IAC Valve ?

My daughter's 94 Ford Eplorer has too low an idle speed and stalls cold and
when making left turns with the foot off the gas.
I was told that the idle air control valve might be bad. I took it off and
it looked reasonably clean. Then I removed the solenoid and I could push
the valve shaft and see it open. The coil measures 9.6 ohms. I assume it
has to push rather than pull the valve. I put 12 volts DC on it didn't hear
any snap as I expected with a solenoid slamming. After I did that I could
shake the solenoid and hear something moving.
How does this valve work and how does one test it?
tnx

--

73
Hank WD5JFR


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Old 10-24-2005, 14:10   #2 (permalink)
Big Shoe
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Re: IAC Valve ?

The computer dithers the valve back and forth by small amounts to
maintain correct idle speed. Problem happens when the valve sticks
shut. Best approach IMHO is to go to a place such as Autozone, buy a
new one and replace it. I cleaned this valve several times on my '99,
but had longer-lasting results when I replaced it.


On Mon, 24 Oct 2005 16:34:05 GMT, "Henry Kolesnik"
<kolesnik@sbcglobal.net> wrote:

>My daughter's 94 Ford Eplorer has too low an idle speed and stalls cold and
>when making left turns with the foot off the gas.
>I was told that the idle air control valve might be bad. I took it off and
>it looked reasonably clean. Then I removed the solenoid and I could push
>the valve shaft and see it open. The coil measures 9.6 ohms. I assume it
>has to push rather than pull the valve. I put 12 volts DC on it didn't hear
>any snap as I expected with a solenoid slamming. After I did that I could
>shake the solenoid and hear something moving.
>How does this valve work and how does one test it?
>tnx

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Old 10-25-2005, 02:02   #3 (permalink)
Henry Kolesnik
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Re: IAC Valve ?

Hey Big Shoe
My daughter says it hasn't stalled yet so it must have been the solenoid
stuck or sticking because the valve itself was pretty clean and move freely
with light pressure. I'll have to wait to see how long it lasts. Does the
ditherer apply 12 volts to the coil?
tnx
Hank
"Big Shoe" <j_shoe.removethis@yahoo.com> wrote in message
news:ccgql19uirto9oc38tkl945dh8duspppp1@4ax.com...
> The computer dithers the valve back and forth by small amounts to
> maintain correct idle speed. Problem happens when the valve sticks
> shut. Best approach IMHO is to go to a place such as Autozone, buy a
> new one and replace it. I cleaned this valve several times on my '99,
> but had longer-lasting results when I replaced it.
>
>
> On Mon, 24 Oct 2005 16:34:05 GMT, "Henry Kolesnik"
> <kolesnik@sbcglobal.net> wrote:
>
>>My daughter's 94 Ford Eplorer has too low an idle speed and stalls cold
>>and
>>when making left turns with the foot off the gas.
>>I was told that the idle air control valve might be bad. I took it off
>>and
>>it looked reasonably clean. Then I removed the solenoid and I could push
>>the valve shaft and see it open. The coil measures 9.6 ohms. I assume it
>>has to push rather than pull the valve. I put 12 volts DC on it didn't
>>hear
>>any snap as I expected with a solenoid slamming. After I did that I could
>>shake the solenoid and hear something moving.
>>How does this valve work and how does one test it?
>>tnx



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Old 10-25-2005, 02:02   #4 (permalink)
Jim Warman
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Posts: n/a
Re: IAC Valve ?

Here's how it works.... but I have to warn up front that "duty cycle" and
"pulse width modulation" may appear to be the same thing - they are not...
It is nigh on impossible to accurately position the pintle of a solenoid
anywhere in between all the way in and all the way out. To overcome this,
the engineers "dither" the solenoid - turn it on and off rapidly so that the
pintle moves around it's desired position. We call this "duty cycling".

Not all duty cycled solenoids are 12 volt solenoids.... some will burn out
very quickly with the application of 12 volts.

Let's start with one cycle... the time period is set by the device (in this
case it is the PCM) controlling the circuit. Just to make the math easy,
let's say the frequency of the circuit is 100Hz (100 cycles per second). One
cycle would last 10 milliseconds. At 0% duty cycle, the circuit is off all
the time. At 100% duty cycle, the circuit is full on. At 50% duty cycle, the
circuit would be turned on for one half of the cycle (in our example, 50
milliseconds) and off for the other half of the duty cycle.

More complications.... Some of these circuits are considered "full on" at
60% duty cycle... applying a steady 12 volts to one of these solenoids will
kill the poor little beastie quite suddenly. Others that do get cycled to
100% wont last long with a steady 12 volts applied but, in their normal
life, they will occasionally get 100% for very brief periods.

These types of circuits are extremely light duty.... It takes time for the
magnetic field to build and decay yet we still need the action to be rapid
to avoid a loping or porpoising effect (if one cycle lasts less time, it
becomes easier to position the pintle more accurately but we have less time
to build the magnetic field. The resulting weaker field can only move so
much pintle). Since these circuits are light duty, it doesn't take much to
"trap" the pintle.... very slight mechanical resistance can make these
controls fail.

HTH.


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Old 10-25-2005, 08:01   #5 (permalink)
Henry Kolesnik
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Posts: n/a
Re: IAC Valve ?

Jim
Thanks for the explanation, I understand what you wrote but that leaves me
with another question. The solenoid is pushing the valve stem against what
I assume is a rubber diaphram at the other end. To get the proper duty
cycle there would have to be some kind of feedback as I assume that the
diaphram resistance could vary with temperture and age. I saw another
device on the same manifold just a few inches in front of the IACV and
wonder if its might be the feedback sensor?
My daughter said the Explorer only stalled once and was so much better that
she asked me what I did. I told her that I thought the solenoid armature
was stuck. She said she could hear some noise when it wasn't working and
now that it wasn't stalling she didn't hear anything. Is it possible to
hear anything inside the vehicle coming from the IAC if its solenoid
armature is stuck?
tnx
Hank
"Jim Warman" <mechanic@tenalpsulet.net> wrote in message
news:VOf7f.57128$ir4.50050@edtnps90...
> Here's how it works.... but I have to warn up front that "duty cycle" and
> "pulse width modulation" may appear to be the same thing - they are not...
> It is nigh on impossible to accurately position the pintle of a solenoid
> anywhere in between all the way in and all the way out. To overcome this,
> the engineers "dither" the solenoid - turn it on and off rapidly so that
> the
> pintle moves around it's desired position. We call this "duty cycling".
>
> Not all duty cycled solenoids are 12 volt solenoids.... some will burn out
> very quickly with the application of 12 volts.
>
> Let's start with one cycle... the time period is set by the device (in
> this
> case it is the PCM) controlling the circuit. Just to make the math easy,
> let's say the frequency of the circuit is 100Hz (100 cycles per second).
> One
> cycle would last 10 milliseconds. At 0% duty cycle, the circuit is off all
> the time. At 100% duty cycle, the circuit is full on. At 50% duty cycle,
> the
> circuit would be turned on for one half of the cycle (in our example, 50
> milliseconds) and off for the other half of the duty cycle.
>
> More complications.... Some of these circuits are considered "full on" at
> 60% duty cycle... applying a steady 12 volts to one of these solenoids
> will
> kill the poor little beastie quite suddenly. Others that do get cycled to
> 100% wont last long with a steady 12 volts applied but, in their normal
> life, they will occasionally get 100% for very brief periods.
>
> These types of circuits are extremely light duty.... It takes time for the
> magnetic field to build and decay yet we still need the action to be rapid
> to avoid a loping or porpoising effect (if one cycle lasts less time, it
> becomes easier to position the pintle more accurately but we have less
> time
> to build the magnetic field. The resulting weaker field can only move so
> much pintle). Since these circuits are light duty, it doesn't take much to
> "trap" the pintle.... very slight mechanical resistance can make these
> controls fail.
>
> HTH.
>
>



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