[xj-s] high idle 86 V12

I just purchased my first XJS. Very good condition, with 68K
California miles, but needs a little sorting out, nonetheless. Once
the car is warmed up I have an idle of around 1500rpms. Cannot seem
to get it down. Any ideas?–
1986 XJS
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In reply to a message from Got V12 sent Fri 22 Feb 2008:

Got v12,

Turn the idle adjustment bolt on the AAV clockwise, and see if you
can get the rpm to 750 on a warm engine.

If not, the piston in the AAV is probably seized open, and allowing
too much air at idle.

A simple test for the AAV is…

Starting from a cold engine.
Remove the B bank outer air box cover, and the filter.
There is a port at the rear of the inner air box that leads to the
AAV.
Start the engine, and let it reach warmup temp.
As the engine warms, listen and feel determine if there is a
variation in vacuum and noise from the air port. Both should reduce
as the engine warms up.

If it stays the same…the piston is seized. Tons of postings in
the search archives on how to repair.

It’s also possible you have a hose vacuum leak, but try the above
first.

SD Faircloth
www.jaguarfuelinjectorservice.com–
The original message included these comments:

the car is warmed up I have an idle of around 1500rpms. Cannot seem
to get it down. Any ideas?


www.jaguarfuelinjectorservice.com
Jacksonville, Florida, United States
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As Dave Faircloth suggests, the AAV (Auxiliary Air Valve), also known
as the Extra Air Valve, is the most likely problem here, but anything
that allows air to enter the intake manifold, such as a vacuum leak,
can cause a high idle. Here is a diagram of the AAV (item 6) and its
connections:
http://www.jdht.com/webapp/wcs/stores/servlet/CategoryDisplay?catalogId=10051&storeId=10051&categoryId=20262&langId=-1&parent_category_rn=20260&top_category=20260

The black rubber L-shaped hose (#4) connects to the back plate of the
left or B bank air cleaner. One test to see if you have some other air
leak is to remove the left air cleaner cover and element, and plug the
port in the air cleaner to which this AAV intake hose connects while
the car is idling. If you have no other air leaks the idle speed
should drop to ~200-300 RPM (yes, it will still run that slow).

The function of the AAV is described in Kirby’s Book. Generally, it
allows additional air to enter the intake manifold, either (1) by the
adjustable idle speed screw, 13mm screw on the AAV air intake (which is
NOT identified by name or number in the linked diagram above, but the
hole for the screw is shown beneath the AAV air intake), or by (2) a
changeable orifice which increases when engine temperature is cold, to
allow more air (similar to choke function in a carburetted engine), but
this opening should close as the engine warms.

Try that and let us know what you find.

George Balthrop, Clifton, VA USA
85 & 89 XJ-S Coupes; 89 XJ40 VDP-----Original Message-----
From: Got V12 bb4re1@yahoo.com
To: xj-s@jag-lovers.org
Sent: Fri, 22 Feb 2008 7:52 am
Subject: [xj-s] high idle 86 V12

I just purchased my first XJS. Very good condition, with 68K
California miles, but needs a little sorting out, nonetheless. Once
the car is warmed up I have an idle of around 1500rpms. Cannot seem
to get it down. Any ideas?

1986 XJS
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

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More new features than ever. Check out the new AOL Mail ! -
http://webmail.aol.com

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In reply to a message from Got V12 sent Fri 22 Feb 2008:

I turned the 13mm bolt all of the way clockwise until it stopped.
This brought my idle down to 1000-1100…from 1400-1500rpms. Would
this suggest a bad piston in the AAV valve, or more likely a leak
in a vacuum line? I will also spray starter fluid at each vacuum
fitting to check for leaks, but would be interested in expert
thoughts on the AAV valve, itself.
Thank you in advance!–
1986 XJS
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In reply to a message from gbalthropxjs@aol.com sent Fri 22 Feb 2008:

I just returned from turning the 13mm AAV bolt clockwise until it
stopped. This brought my idle down from 1400-1500 to 1000-1100.
Would this suggest a problem with the AAV piston, or more likely a
vaccuum leak somewhere? I will check all of the vaccuum lines, as
well…just wondering if this result might show a condition of the
AAV piston.–
1986 XJS
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Got V12 wrote:

I turned the 13mm bolt all of the way clockwise until it stopped. This
brought my idle down to 1000-1100…from 1400-1500rpms. Would this
suggest a bad piston in the AAV valve, or more likely a leak in a
vacuum line?

It doesn’t provide any info on that question. Remove the cover and
element from the LH air filter housing and start the engine. Put
your thumb over the hole leading to the AAV. If the engine speed
drops just a coupla hundred rpm, your problem is a vacuum leak
somewhere. If the engine speed drops a lot, like down to under 300
rpm or even dies, then the problem is in your AAV, the piston is
stuck in the open position.

I will also spray starter fluid at each vacuum fitting to
check for leaks, but would be interested in expert thoughts on the AAV
valve, itself.

Just for grins, tighten down the 24 nuts holding the intake manifolds
to the engine.

– Kirbert

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In reply to a message from Kirbert sent Sat 23 Feb 2008:

u can also try using a rubber drain stopper with 1/4’’ hole drilled
thru it to plug the AAV hole in the air-box as a temporary fix…–
Lead 88 XJS V12 HE Coupe
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