So, I've been sporadically having the "rev hunting" issue when in park or neutral, and after much searching on the forums, am quiet sure that the AAV is the culprit.

In preparation for rectifying this issue, I've downloaded the write up from the Wizard Of Oz on how to rebuild the AAV, but I am also curious as to whether doing away with it altogether may have any negative consequences on the engine?

If my understanding is correct, its purpose is to allow that extra air in to raise revs while cold, until the engine warms up to a certain temperature, then the valve closes to cut off that extra air.

Would simply locking that valve into a permanent closed position serve as a suitable bypass?

And also, if I were to get fancy some day down the road and want to use a manual solenoid to replace the AAV altogether, so I could trigger the higher revs in extreme cold, would any 12v solenoid with a closed off position do?

Thanks in advance for your input!

 

That's it !



Yes.

Many AAV are locked in the closed position with no action taken by the owner at all. I've had that situation on both my V12s. No ill results in my experience. The lack of high idle speed when the engine is cold only presents a problem when ambient temps are outright frigid. In those cases the function of the AAV is replaced by your foot goosing the throttle pedal of a minute or so.



I would say so, yes. In fact, the Extra Air Valve in the RH air filter housing would be a good example

Cheers
DD

 

Here is a writeup on what I did. Works wonderfully well. The solenoid I eventually used was from the 6 cylinder 3.6 litre XJS, a genuine Jaguar part.
I have since found a suitable T shaped hose with a 13mm ID leg of the T, and it would now be even simpler to install the solenoid into the 1 inch balance pipe between the banks that the AAV feeds into. Just replace the balance pipe joiner hose on B bank end of the pipe with the T piece and plumb the solenoid into that. Then the feed pipes to the manifold/throttle body can be dispensed with, and the V will be less cluttered.
The advantage of this mod is that the AAV tickover adjustment stays as OEM.
Greg

 

Simplicity would be to clean out the AAV and have it working properly. They do work well, and are generally reliable for most people.

Removing as per Greg is also a good idea, as it leaves the AAV in place, so the air bleed for HOT idle adjustment is still as designed, which is also simplistic for most owners. The cold start extra air that will be needed can be achieved as per Greg again, or any solenoid that is closed with no power, BUT, it will need a suitably sized internalbore to give sufficient air for cold start. OR, elcheapo version, a few seconds of manual holding of the throttle by the driver will suffice. Since we dont get Gregs Winters here, maybe a goer.

The air con kick up solenoid in the backing of the RH air cleaner is suitable, IF, you have 2 of them, That is what I used.

The other thing that can/does cause idle hunting is a TPS out of idle range, and the infamous V12 Black Goo inside the throttle bodies.

Drop the AAV from the other XJ-S over the back fence, and I will clean it for you, then swap them for now, until you decide which way you want to go.

 

Won't it be possible to rework the AAV using the same housing and make it electrical rather than mechanical?

Say using a solenoid and temperature sensor (which can still use the coolant temperature in that area) to control it? I'm sure a few experts here would be able to make something up... A few wires then to the ignition switch (key) and then it would probably be a durable, reliable piece of kit looking original...

Just my €0.02

 

I'm going to give the rebuild as per your instructions a crack this weekend, gotta learn how to do these things on my own eventually

Does leave me thinking though as you have said that we don't really have those ridiculously cold winters and holding my foot at 1300 rpm for a minute or so isn't such a struggle, doing as Greg has stated in his above post about closing off the AAV but leaving it intact to fine tune idle at normal engine temps could also be an option.

Regardless, will be a fun way to spend half my day on a weekend! (Better than removing that PITA immobiliser!)

 

I've had once the cold revving issue (so, AAV) on my AJ6.
Weather was cold and I must confess that I don't drive it often; it happened after a month sitting in the garage.
It seems that it is occasional since I did not have it since then, though I let the cat sleeping for several weeks between rides.
Question: if the piston did not slide easily once because of some surface degradation, is it possible that it can "heal" itself when the engine is reused more often? Or should refurb be considered at some stage?

 

You know where I live, just yell out if you get stuck.

 

Purely depends on what caused the issue in the first place.

Most V12 units are from lack of use in MY opinion, followed very cloesly by carbon deposits finding there way in there.

Most I have dismantled had the alloy piston, and are quite scarfed with some sort of Black Grit.

One I did, had a Stainless piston?, and although gritty, the piston was unmarked, but the grit was imbedded in the alloy bore, so same sticking complaint.

You gotta watch the honing, coz if the clearence between the piston and the cylinder bore is too "free" then vac leaks will negate the whole system.

The "slide style" on the S3 6 cylinder seem to be less troublesome, and do tend to self clean as they are used, and I believe that sliding disc action does keep them cleaner.

 

Nice write up on the replacement Greg. I wonder if two supplemental air valves would be sufficient? So, if you added one to bank B and on cold starts activate the original A and the secondary B, would that be sufficient airflow to maintain idle at cold temperatures?

 

Thats all I used on teh HE.

The PreHE got 2 fuel solenoids, the ones in the rear wheel arch of the Series cars, and although a tad slow in the dead of winter, still more than acceptable.

One here used a solenoid of some sort he found at a scrappers that came from an Audi. Its not that critical, not worth over thinking the whole process, as long as the engine sees extra air when stone cold, and that air can be shut off when not needed, job done.

 

They will be, but one larger-bore one as I used will do it, but it must be fed to both banks. I have recently found a 1 inch diameter T hose with a 1/2 inch leg on the T silicone hose, and I am going to replace my manifold twin feed arrangement with this piece that I will fit in place of the B bank to rear of the engine balance pipe joiner hose. Then plumb the solenoid into the leg of the T and clear the current hoses out of the V.
Greg

 

Hello again!

Thank you all for your input and I can't wait to get cracking on this job tomorrow.

I just had a few questions in regard to Greg's modification to the AAV as per the image lifted from his write up below:


In the above set up where the cold start air passage has been sealed off by rotating the cylinder and applying epoxy to make the seal air tight, since the piston has been removed altogether, and the piston itself does contain holes to allow the passage of air even when the valve is closed at operating temperature, will doing this modification and leaving the piston out result in more airflow coming through the tickover/idle adjustment air passage, as it it will no longer be impeded by the piston itself? If so, will there be enough adjustment via the tickover/idle adjustment bolt to compensate for this? Or will this extra air coming in from the smaller tickover/idle air passage unimpeded by the piston pose a problem in and of itself?

Thanks in advance!

 

It will not. There are large holes in the bottom of the piston which allow the tickover air through it. The adjuster on the tickover channel in the AAv works normally to adjust the airflow.
Greg

 

Thanks for the quick reply and putting my mind at ease, Greg! Your input is greatly appreciated, mate!

 

Do not use any of these "quick dry" epoxies. They generally return to liquid at "about 100C", not good.

I use Original JB Weld, 24 hour dry time.

 

The mechanic's best friend


Cheers
DD

 

Thanks to everyone who has contributed to this thread.

I am glad to report a successful repair and the beast is now purring gently when resting instead of growling.

In the end, wound up just blocking off the hole from the cold start air passage into the cylinder using a nut with a hole roughly the size of the hole in the cylinder, and using the cold weld epoxy to fill in all the gaps around the nut with the cold start air passage to form a seal, being careful not to cut off the tickover air passage. Then threaded a shortened bolt into the nut to seal the passage into the cylinder. No more air into the cylinder, but can still use the tickover adjustment, and still have the option of taking the bolt out of the nut should I ever need to unjam the piston in the AAV and use it as intended (which I can't ever really see myself needing to do).

I couldn't get my hands on the JB Weld as apparently my local SuperCheapAuto don't stock it, but wound up with a same cost alternative that should fit the bill, keeping in mind the high temperature resistance issues that other cold weld epoxies have:

Here's hoping it lives up to it's claims!