[Fwd: Re: Testing an ISV]

[John Sherrow]

I'll defer to Tom's larger sample size. My observation on air passing
thru the "bad" ISV was based on a sample of two, one good, one bad.

As I recall the ISV was capable of opening to varying degrees. You need
to be able to precisely control the current though. I believe this is
what the idle contoller does to raise the idle speed at cold,under a/c
load etc. All PWM does is supply a higher or lower average current to
the solenoid moving the disk slightly wider open.

I would also agree that w/o a vacuum source and appropriate test
equipment there's no sure way to verify its operation other than
swapping it. I could make the bad one operate over the full range of
motion but it could not stop the engine from pulling air thru it.

BTW, my car idle oscillated whether or not the ISV was plugged in.



-------- Original Message --------
From: Tom Christiansen <tomchr at ee.washington.edu>
Subject: Re: Testing an ISV
To: quattro at audifans.com

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