[s-cars] Idle stabalizer valve (ISV) - how does it work?

[Mike Fitton]

Someone correct me if I'm wrong, but my understanding is this:

Pneumatically, the ISV sits in the intake system with one side hooking 
up before the throttle and the other side hooking up after the 
throttle.  Airflow is controlled by a rotating valve operated by a 
solenoid.  When the throttle position sensor tells the ECU that the 
throttle is at or near fully closed, the ISV circuit becomes eligible 
for operation.  The ECU pulses the solenoid on a duty cycle, I assumed 
timed to coincide with each cylinder's intake stroke.  Near the time 
when a piston begins moving down on intake, ECU opens the valve allowing 
intake air to bypass the throttle plate.  By precisely timing the 
operation of the valve, the ECU is able to deliver precisely the amount 
of air required to sustain the exact idle speed.  Of course it's still 
dealing with the whole gasoline side of things simultaneously and to the 
same end.

That's the quick and dirty.  Can't tell you anything about exact timings 
of the cycling or whether or not it cares about crank position during 
all this, nor any good data on the ramp profile of the airflow due to 
such rapid cycling.

-Cheers!
Mike

chris chambers wrote:
> Gentz,
>
> Previously the car's idle would "pulse" up and down, I cleaned the
> ISV with carb cleaner and it idled better but not "right".
>
> Apparently I have a defective ISV, wondering how it works.
> With the ISV's wires plugged in the car won't idle and dies when
> the throttle isn't pressed. Unplug the ISV's wire and the car idles but
> I get a check engine light.
>
> Nothing else was unplugged on the engine, I know some people have
> plugged a different cable in to the ISV and the car ran bad, this
> isn't the case.
>
> Is the ISV servicable or does it need to be replaced?
>
> Make April 15th just another day http://www.fairtax.org
>
>
>
>       
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