Possible to bench test an Idle Speed Control Valve?

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scott21230@gmail.com - 05 Mar 2008 20:05 GMT

I just replaced the one on my car, a 1995 Escort, and I'm curious as
to how this thing is supposed to work. the resistance across the coil
is right, but when I apply voltages to it (anywhere from 8-25V DC) I
really don't see anything resembling what I'd expect to see, but I do
feel the coil being energized. If necessary I can send it a square
wave or sine wave signal, etc., but I can't find anything on the
internet explaining how it's supposed to work or exactly what I'm
supposed to see. When energised I do some some movement in the parts,
but not much. Obviously the part is bad because it fixed my idleing
problem immediately when I replaced it, but I'd like to learn
something if there is something to be learned before I throw it out.

Note: It had been cleaned maybe a year ago, and so I don't think it
was that dirty. Possibly the reason I'm not seeing it do much is
because it's broken.

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clifto - 05 Mar 2008 21:53 GMT

> I just replaced the one on my car, a 1995 Escort, and I'm curious as
> to how this thing is supposed to work. the resistance across the coil
[quoted text clipped - 4 lines]
> internet explaining how it's supposed to work or exactly what I'm
> supposed to see.

It's pulse-width modulated.

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Steve W. - 06 Mar 2008 05:39 GMT

> I just replaced the one on my car, a 1995 Escort, and I'm curious as
> to how this thing is supposed to work. the resistance across the coil
[quoted text clipped - 11 lines]
> was that dirty. Possibly the reason I'm not seeing it do much is
> because it's broken.

It is nothing more than a solenoid with a monitor circuit in it. Throw a
square wave through it at 12 volts and it should extend and retract on
the pulses. It doesn't move much. Usually they no longer send the signal
back to the ECM so it cannot control it properly.

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Steve W.

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scott21230@gmail.com - 07 Mar 2008 01:21 GMT

> It is nothing more than a solenoid with a monitor circuit in it. Throw a
> square wave through it at 12 volts and it should extend and retract on
> the pulses. It doesn't move much. Usually they no longer send the signal
> back to the ECM so it cannot control it properly.

It only has two wires going to it, so you are correct on the no
feedback part. I can input a square wave to it.
Yes, when I was applying straight voltage it only worked when i
applied voltage in the correct polarity.

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sdlomi2 - 07 Mar 2008 02:30 GMT

>> It is nothing more than a solenoid with a monitor circuit in it. Throw a
>> square wave through it at 12 volts and it should extend and retract on
[quoted text clipped - 5 lines]
> Yes, when I was applying straight voltage it only worked when i
> applied voltage in the correct polarity.

It is supposed to send a signal back to ECM so ECM can adjust voltage to
it to properly control idle speed--it is when 'broken' that it no longer
sends the signal back. It is probably grounded when in place(1 "wire"), a
"2nd" wire controls it from ECM, and "3rd" wire is to send signal back to
ECM. s

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Steve W. - 07 Mar 2008 04:26 GMT

>>> It is nothing more than a solenoid with a monitor circuit in it. Throw a
>>> square wave through it at 12 volts and it should extend and retract on
[quoted text clipped - 10 lines]
> "2nd" wire controls it from ECM, and "3rd" wire is to send signal back to
> ECM. s

Yep. You have it correct. Just like most vehicle until the companies got
smart and started using ground wires to components to get cleaner signal
return.

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Steve W.
Near Cooperstown, New York

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Scott Dorsey - 06 Mar 2008 16:26 GMT

>Note: It had been cleaned maybe a year ago, and so I don't think it
>was that dirty. Possibly the reason I'm not seeing it do much is
>because it's broken.

Bingo! It's a solenoid that should open a little valve, but it isn't.
Either because the valve is jammed or the solenoid has some shorted turns.
--scott

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