Testing an ISV

[Tom Christiansen]

Hi,

>   I am wondering if anyone has a little howto on testing the ISV on an
>87 4kq.  I looked at, cleaned it, and I still think it is a little
>funky.  I was wondering what and how much voltage to apply were to
>verify that it is working correctly.  Any ideas?

As someone said, apply 9-12V to the terminals and see if it operates. If
the thing moves around in there, at least there's a chance that it works. I
recently cleaned my ISV. I made sure it operated when a voltage was
applied. But then I put it back on the car, and the idle in closed loop
started oscillating between 1400 and 1600 rpm. I unplugged the ISV which
caused the idle to be a bit rough, but stable, at 1000-1100. Then I changed
the ISV and the problem went away.

So to make a long story short, I don't thing there's a sure way of telling
if the ISV is bad or not. But if the problem goes away when you unplug the
ISV at least there's a relatively high probability that the ISV has gone bad.

Someone on the list - John Sherrow - suggested that a problematic ISV will
allow air to pass from inlet to outlet when the ISV is closed (no power
applied). But on both my ISV's (the good and the bad) air will pass through
the valve without applied power. I suppose that's why there's a crack open
on the ISV disc...

For more info read the "Audi 5000 idle problems" thread.

Thanks,

         Tom