Very High Idle ISV Problem

[Christopher Flanner]

Yup, idle switch checks out.  I went through each step in the Bentley for
troubleshooting idle stabilization problems and everything checked out okay.

Wouldn't a bad idle switch only affect ISV control?  The idle is 3000 rpm
even with the ISV disconected!






>From: JShadzi at aol.com
>To: cflanner at hotmail.com ("Christopher Flanner"), quattro at audifans.com
>Subject: Re: Very High Idle ISV Problem
>Date: Mon, 17 Feb 2003 11:34:10 -0500
>
>*sounds* like a bad idle switch, have you confirmed that it works?
>
>Javad
>
> >Listers,
> >
> >My 90tq decided to act up on the way to dinner Friday night, challenging
>me
> >to parallel park with a 3000 rpm idle. =A0The engine is an MC from an '86
> >5ktq. =A0The throttle valve is fully closed and the idle returns to norm=
al
>if
> >the ISV hose is pinched shut. =A0I opened the ISV and it wasn't sticking
>open
> >but I cleaned it anyway. =A0It seems that the pressure differential over
>the
> >ISV is sufficient to open it. =A0While it's idling at 3000 rpm the vacuum
>is
> >about 4 inH2O higher than regular idle at over 22 inH2O.
> >
> >I don't have a clear picture of the idle air bypass layout in my head but
>is
> >it possible that the screw-adjusted bypass is blocked causing vacuum to
>open
> >the ISV valve? =A0I tried to blow and suck through the ISV (smart, I kno=
w)
>and
> >it is very much closed but when the engine runs/idles there is definitely
> >air passing through it even when it's disconnected (electrically). =A0I
>won't
> >mention that I got an oily piece of junk caught in my throat when I tried
>to
> >perform CPR on the ISV. =A0Oops, too late.
> >
> >My ISV isn't receiving any signal but I don't think that's my problem.
>=A0If
> >the connnector is disconnected on an ISV it should stay closed, right? =
=A0I
> >went through the Bentley ISV diagnostics (which aren't for an MC but most
> >details are similar) and everything checked out leading to the
> >recommendation of replacing the control unit. =A0Once again, I don't thi=
nk
> >that's related to my problem since having no signal usually leaves the
>valve
> >closed.
> >
> >Summary: =A0The ISV moves freely and is normally closed but when the eng=
ine
> >runs, it is apparently open, even though it is disconnected, and causes
>the
> >engine to idle at 3000 rpm.
> >
> >What's going on?????
> >
> >
> >
> >
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