Re. No Idle

Ben Swann benswann at
Wed Dec 3 09:54:00 PST 2008


You likely have a problem with the Idle Stabilization circuit - like it is not being
enabled to run in closed loop operation.  Closed loop operation is enabled by the switch
on the throttle body.  Those wires are a common failure point.  Also the switch tends to
get out of adjustment and/or just fail, but more likely adjustment.  You should hear a
definate click when opening and closing the throttle near idle.  You can test the switch
to see if it goes continuous - ref Bentley diagram, but my money would be on the wires
under the rubber fboot at the switch connctor -  Fairly easy repair.

For ECU pinout if you don't have Bentley, see:
and you'll have to match the wire colors at the ECU.  Or just test one side to
ground(brown)  then the other with VOM, since one side is WOT( wide open throttle) and
the other idle.

You may have problem with wiring at the ISV.

Usually the ISV fails more in an open manner or gets flaky/stuck causing idle hunting or
bounce, so I don't suspect it, although you might clean it after the repair.

BTW don't mess with the adustment screw unless emergency.  The screw is set proper and
unless you made major engine changes, idle should be maintained in operating range.  If
the engine is stalling regularly then there is another problem that needs to be fixed as
ISV was working around the problem.  Sounds like a full tuneup may be in order.  Proper
starting and running at idle is dependant upon Idle switch closing as not only is ISV
circuitry affected, but so are ECU - timing and fuel at idle AFAIK, so more and more
sound like throttle switch ot wires.


[Date: Wed, 03 Dec 2008 07:34:11 -0800
From: JeffreyZentner at
Subject: No Idle
To: quattro at
Message-ID: <1228318451.4936a6f3e9f89 at>
Content-Type: text/plain; charset=ISO-8859-1

Hi All
I drive a 87 5000 Turbo Quattro daily. This morning when I went to start it, it
would not idle. Sometimes it runs a little ruff in the morning but this never
changed. The one thing I did last night was to add more oil. This morning it is
hard to start and if I take my foot of the gas and the RPM go below 1000 the
engine will die. I have looked for wires I might have pulled off when adding
oil but I do not see any. I looked at what I think is the idle adjustment screw
in the front of the turbo housing and it is still there. When I try to start it,
it is like the fuel from the pump is there but it will not continue to run
without just the right amount of gas at just the right time. What has gone

Jeff Zentner

Alta CA

87 5TK]

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