re. high idle....5ktq ... a little help please

Thu Sep 27 13:40:06 EDT 2001

[Problem is car is running high idle after warming up, push the clutch in
while slowing down from 40-50 mph and the rpms stay at 2500-3000.  Tap the
throttle and they slowly drop down to a slightly more nomal 1200 or so.  If
i keep playing with it I can get it to drop to 900 or so.  I browsed the
archives and saw either a leak in the vacuum hoses or a dirty/malfunctioning
Idle Stablelitzation Valve.  I'll look for the vacuum leaks tonight, but I
think its going to be the valve.  I'm going to try cleaning it with carb
cleaner while actuating the solinoid.

Question is.... any other possibilities here?  Or are these 2 the most
common reasons?

Thanks

Rob
86 5ktq]

Rob,

Some other things to search on:

disintended nondeceleration

Idle speed oscillates

4KQ Idle wandering

temp sensor and o2 sensor

poor running 200Q

High Idle problems ..5KTQ - solved

Idle switch/Assembly - 4KQ

High Idle problems - did not go away while I was gone.

________________________________________

Here is the excerpted post of my past experience:

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.

Thanks for the various replys on this.

Ben Swann

Recap of the symptoms -

5KTQ.  We can rule out the throttle body (idle/WOT)switch. *** note I had
checked the switch and even replaced though it seemed ok - didn't think to
look at the wires ***

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.

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.

*************
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.

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.

..
________________________________________

Ben Swann
'87 5KCSTQ - Boosted! And going for more..
http://www.homestead.com/Ben_Swann/myaudi.html
'85 4KSQ - Jamex, Boge TG's all new rubber, and Stebro SS exhaust 264 CAM.
'86 4KCSq & '90 80(nonQ4cyl) - parts cars - I might have what you need
'85 4kCSq - Colbalt Blue - for sale - wish I could find one this nice in
white or silver, maybe black and leather interior!
http://www.homestead.com/Ben_Swann/ColbaltQ.html
I'm looking for 80/90Q with 2.3l or 4KQ in as good shape as the blue one I'm
selling, just different color. Engine doesn't have to run, but body near
perfect and good leather interior(preferred).