86 5KTQS High Idle Problem (and others)

[Ben Swann]

Yes we have and it can be caused by numerous things - sorry about the
length of this.

Some things I have found, having been through this frequently on 3 out of 3
5000 turbo quattros in 4 years.

- WOT switch/circuit failure would cause a high idle.

- A failure in the wiring to the Stabilizer will cause RPM to drop/engine
stall

- A failure in one or more the temp sensor/wiring will cause RPM to
drop/engine stall

- The decel valve opens by the switch and closes at 1200 rpm - allows the
plate to
settle to the rest position. You can actually hear it open as rpm winds
down.  This could kill the engine..would not start troubleshooting here.

- Check under rubber boots on what looks like good wires to suspected
switches/valves.  This is especially relavent if you just got finished
doing some work around the connector.

- Bently wiring diagram  - invaluable, but sometimes hard to follow.  A
thin horizontal line running through several wires with circle next ot it
is a welded wire connector - wires are connected, likely share a common
source.

See below for more extensive explanations and embedded comments.

Ben

[From: "Haydn Taylor" <haydn_taylor at hotmail.com>
To: quattro at audifans.com
Subject: 86 5KTQS High Idle Problem (and others)
Date: Wed, 23 Oct 2002 17:38:43 -0400
<snip>
Towards the end of last winter I noticed the idle speed creeping up, then
spring came and the problem seemed to dissapear. As the outside air temp
has
begun to decrease again the idle problem has returned. The car now starts
up
from cold with a normal(ish) idle of about 1200rpm, as the motor warms this
builds to approx 2000rpm. When I then drive and stop again, the idle is at
about 2200rpm, it then hunts up to approx 2600rpm, then after approx 5
seconds drops back to 2200rpm, this cycle then continues, after a couple of
minutes the idle will sometimes fall back to about 1800.the thing that is
really getting me confused is that if I slip the clutch to bring the engine
down to say 800rpm, sometimes when I fully depress the clutch again the
idle
will stay down at 1000, and other times it will go back to it's hunting
game
up at 2200.

I have noticed the problem is noticably worse on cold days.

I have also noticed a puff of white smoke on startup that is getting worse,
and a drop in fuel economy - making me think about leaking injectors (I
bought a new set at the weekend but have not fitted them yet)

**** this will cause hard starting, but not idle problem ****

My only other thoughts for the cause are
A. Oxygen Sensor dying  **** NO  ***

B. Temperature sensor somewhere not functioning correctly -  *****remote
possiblility  ****

C. Vacuum leak somewhere -  ****** Possibility  *******

finally the only other thing I have moticed that is odd and sort of relates
to the heater controls. with the heater set to 'econ' the idle is a little
lower (1800 ish), and with it on max, the AC clutch kicks in for about 2
second duration every 10 to 15 seconds, and the idle is even higher.

**** heater/AC deals with Idle, but not likely problem ****

Any thoughts on this would be greatly apprecated before I start tearing the
thing down again next weekend.

Yours most sincerely

Haydn]

OK here is a recap for this problem, since it has not been discussed in
awhile, and not in recent archives probably -

<Beginning of recap on High Idle Problems troubleshooting.>

Greetings,

I only got replys from one lister on this.  I sure would appreciate some
additional help based on experience, esp. with the 5KTQ.  We can rule out
the throttle body (idle/WOT)switch.

**** NOTE: I replaced the switch, even though the old one checked out fine

**** NOTE:  Switch is the among the first things to check

I dont have the Bently on me right now, but a part of my confusion may be
the way the diagram shows the wires going to the idle/WOT switch and other
sensors including the decel valve.  The diagram shows a thin line going
across two or three wires at a time in several places esp. coming of around
the ISV conrol unit and also the switch and associated wires, in adjacent
current tracks.  It is unclear whether this means the wires are actually
connected, or this is just representing that they a collectively part of
the same part of a harness.

**** I was on the right track here, but is was far simpler

Is the decel valve know to cause this kind of madness.  Is the +12V  that I
don't get at the idle switch supposed to be coming from the decel valve, or
is it the other way around, and I should be looking for a breakdown
somewhere else.  I'm poring over the Bently manual and see several tests,
but some guidance as to exactly where to resume troubleshooting could save
 much time.

So I therefore greatly appreciate input from someone who may have been
through this already, and/or has a thorough understanding of the ISV system
and can steer me in the right direction.  Once I get this resolved, I will
gladly post results of what may be a compound problem.

TIA again.
*************
Recap of problem below with additional info as I progress with
troubleshooting..>>>
<SNIP>
I just got back from a 3 week vacation in Peru - <SNIP> still chasing high
idle problems on both cars.

'87 5000 Turbo Quattro Wagon idle has progressively worsened.  Idle after
warmup ranges from 1200 to around 2200, holds fairly steady and will slowly
drop down to 1200 - 1500 RPM.

To recap details on symptoms:

I dont believe there are any airleaks, as I've been over this engine
thouroughly.

I noticed if I force the RPM to drop by putting in gear and loading the
engine, it will hold the lower idle(somewhat), but will generally bounce
back up to around 1200RPM if forced to lower RPM.

Idle/WOT throttle switch OK/Questionable(REPLACED), but  bypassing = no
difference.
As suggested, I replaced the Throttle position switch(replaced because
readings were more like 10-20 ohm rather than 0 ohm on switch closure, and
some perceived flakyness) on the 5000TQ to rule it out, and as suspected it
made no difference at controlling idle (may have improved possible WOT
operation however).  SWITCH OPERATION VERIFIED

There is NO VOLTAGE to pin 2 on center connector.
According to Bently, if no 12V then check wiring.  Referred to wiring
diagram and confirmed there is voltage at Idle control unit terminal
15/SAS.
As I mentioned in previous post, THERE IS NO 12V on the connector pin to
the switch, but the control unit is providing 12V at the appropriate pin at
the relay panel, and when the switch closure is simulated, there is no
difference, and that there is no voltage to the switch when ignition on, as
specified in Bently.

**** NOTE:  This methodical toubleshooting is good in that it will
ultimately lead you to the answer in time, but sometimes you end up
regretting tearing things apart, especially when the culprit is right in
front of your nose.

Bently diagram shows(if I read it correctly) this goes to the Decel Fuel
Cutoff Valve first then voltage goes to the throttle switch connector pin
2.  There is voltage going to the connector to the decel valve.

I pose these questions again in hopes someone has dealt with it: Is the
decel valve the culprit?  Should I check something else?

It is a pain to get to (and very expensive at dealer), and I don't want to
purchase new one and pull out the entire FI assembly without reasonable
certainty it is the problem.  Doyt Echelberger mentioned it was accessible
from under the wheelwell, which I can try, but still it is an expensive
part.  I already did shotgun troubleshooting with the throttle switch.

Any BTDT on this.  Any clarification on how the Idle stabilization circuit
works(is supposed to work), esp. with resp. to decel valve, would be
helpful.  The system seems to be in some type of feedback loop state where
the higher the idle is after taking out of gear, the higher the idle stays,
eg. if I drop the idle to 1200, it will stay there.  Can't seem to get it
any lower than that after warmup however.

Also, if I disconnect ISV momentarily, Idle drops to 500ish and stays there
when reconnected which I understand is Normal.

<snip> Sorry about the long post - just trying to give a thourough
explanation of symtoms and diagnosis thus far.

Ben Swann

*** AND THE ANSWER was  ****

-----Original Message-----
From:	owner-quattro at audifans.com [mailto:owner-quattro at audifans.com] On
Behalf Of Swann, Benjamin R.  (BSWANN)
Sent:	Monday, February 14, 2000 9:21 AM
To:	'quattro at audifans.com'
Subject:	RE: High Idle problems ..5KTQ - solved

It turned out to be quite simply the wires going to the connnector at the
ILDE/WOT switch were broken.  I should have checked under the connector
rubber boot in the first place, but I guess these types of problems always
seem trivial once they are fixed.

Wiring diagram prompted me to look for this, as the center conductor of the
connector should be 12V coming directly from the Ignition circuit.

Car idle nice now - solid 750 RPM.

Lesson learned - the wires at the connectors can fatigue and fail which is
not evident unless you peel back the ruber boot covering the wires. on
mine,
three out of four wires were disconnected/broken.

<End of recap on High Idle Problems troubleshooting.>

Now with all of that regurgitation, I have found the most common culprits
to be:

1 - The Idle Stablizer Valve

2 - The WOT/IDLE switch located on the throttle body

3 - The idle screw located on the throttle body (air leak due to hardened
o-ring)

4 - nebulous anomolies which coincide with position of the moon, and
sunspots ( things like partial ignition switch failure and the broken wire
at the switch)

Hope all of this helps.

Ben