Since it is cold here now in Chicago my 1988 XJS V-12 with 48,000 original miles has started a new headache. When engine is started from cold the RPMs are around 1500 a nd never come down. I did some research here and seemed like the AAV may have needed some attention. I did as outlined by one of the "old sages" outlined here. I removed the AAV and put it in boiling water. The AAV did nothing so i took it out and cleaned it and lubed it. I put it back in boiling water and it closed properly. I took it out and ran it under cold water and it opened properly. i thought i found the fix...but no. After i reinstalled it on a cold engine the RPMs are at 1500. When engine is warmed up the RPMS are still that high. I am very good mechanically if i have to repair something broken, but i am TERRIBLE at FINDING the problem. ANY help would be more than appreciated!

 

This may be a dumb question since you probably tried it but have you adjusted the screw at all? There is a cold idle adjustment on there youll need a wrench.

 

If you've adjusted the screw and nothing happens, then your AAV may be on the way to permanent failure. Mine did that earlier this year, so I just ditched it and improvised a system where I can flip a switch in the passenger compartment and it opens an air valve which is plumed into the crossover pipe. Opening the valve raises the RPM at start to speed warm-up. Then after a few minutes I just flip the switch off and all is good. The down side of this method is that the only way to adjust the idle is with the butterfly valves. While it's a bit of a pain, I don't need to do it that often, it's sort of a "seasonal" adjustment.

Your other option is to buy a replacement AAV, but those are not cheap.

Just south of you (in Indy),

John
1987 XJ-S V12

 

Bert,

Welcome to the Forums.

When time permits, please do an Intro in teh New Members Area.

Your AAV is maybe sticking in real life application,

BUT

You also more, than likely, have a huge air leak.

Most common is the 90 deg elbow on top of that AAV. They split on the underside, and since you have been at it, is a prime suspect.

The list goes on and on, but its usually simple enough IF, you take your time.

That "bolt" on the side of the AAV is NOT, and I repeat NOT, a cold idle speed adjuster. That Cold idle speed is set by the AAV assembly and the cut outs insde the intake snout.

That :bolt" is the HOT idle adjustment, IF, you dont have other issues, like air leaks into the vac system.

Some markets, ours was one, got a 15 minute timer fiasco that held about 1300rpm +/- when cold for that time frame, and most have been deleted by simply unplugging them.

These might help.

 

Hi, and yes. Screwed it bothe all the way in and then all the way out, but it did nothing. I did plug the sucking hole in the air cleaner housing. It reduced the RPM by maybe 200rpm"s. But i know that is not the solution and it didnt help enough anyway. More thoughts?

 

Hi, thanks for the reply. I would try something like you did, but i'm not smart enough to figure that ou. Have you any suggestions on where i might find a good used one? What i really don't understand is why it worked in the boiling water then cooling it quick, many times. Then i put it back in the car and nothing.

 

Thank you for the help mate. I know the nut on the side of the AAV is NOT for cold idle adjustment, but i did, out of sheer frustration screw it all the way in and out. It obviously changed noting. I do have the green cover "Repair Operation Manual" which i consult before i try to "fix" anything. The manual was written for tech's who know their way around the XJS. Sadly i am not one of them. After reading a topic i am still most often at a loss. There are NO air leaks anywhere on the engine. One reason i bought this car, from a friend who's dad died and left him the car, is that his father kept it housed in a climate controlled garage. All the rubber and leather is still very supple. I share that only because in looking for air leaks it is much easier because if that history. The car even had the original factory tires. They looked brand new with only 48,000 miles. ANYway is this any help?

 

Hey guys trying to help me here. PLEASE be a bit patient with my posting of replies as i have never done this before. I am SURE i posted or responded incorrectly, and for that i apologize.

 

I see now i should click the "quote message in reply" so everyone knows to whom i'm responding. I'll do that from here out ;-)

 

I will also look at and print out all the doc. links you sent me Grant. THANK YOU very much!!!

 

Hey Grant, What does "TPS" stand for? WHAT is the TPS? The links you included are superb! Thanks again!

 

The reason turning the adjuster screw , or plugging off the sucking hole, doesn't make any difference is that you have more air coming in from elsewhere.....as Grant said. Either A) an air leak or B) the throttles are not set right or are sticking.

The AAV and adjuster screw are themselves nothing more than controlled air leaks.

In this type of system the engine doesn't know or care where air comes from. If more air comes in, the engine speed will increase. That's pretty much the long and short of it

Recently on my V12 I had a high idle problem. A sticky throttle cable was holding the throttles open a tiny bit. The clue was that the idle speed dropped when the cable was disconnected.

Cheers
DD

 

Throttle position Sensor. It's a potentiometer placed in the capstan tower sending a voltage signal to the ECU. 0,32V is idle, 5V'ish is fully open

I had a fair amount of air coming throug the crankcase vent valve connected on front of LH airbox. Blocking that lowered my RPM 150-200 (warm). I modified it by preloading the spring a bit more, that was the final thing that made my RPM settle correctly.

BR Leo

 

You may be able to find a used AAV on EBay or such. Of course you have no guarantee that it will work correctly, or that it won't fail shortly after installation since it's likely to be a used part.

You may want to look here: Bernard Embden's Jaguar Website

He removed his AAV and put a push/pull cable (like the "choke" that older cars had). He seems to be something of a perfectionist, but you could do the same thing with much less work.

If you don't feel up to something like this, you may just have to replace the AAV. Not cheap, but you might be running out of options.

John
1987 XJ-S V12

 

Remove the air filter on the same bank as the AAV.

There is a hole about the same size as a table tennis ball toward the rear air filter housing feeding the AAV.

Run the engine at idle and block the hole temporarily.

If the idle slows down you have a faulty AAV.

If it doesnt you have a split hose somewhere.

Craig

 

OK. there is 100% air getting in somewhere.


With that hole plugged, and ALL the culprits eliminated, plugging that hole WILL stall that engine, fact.

Doug mentioned the throttle cable/discs, and that is a good place to start.

If the TPS (Throttle Position Sensor) was that far out of range, the thing would be belching black smoke.

I will sort a list when i finish work, and you can work through it slowly and systematically, which is the ONLY way to sort a hissy V12.. Working on these without a system will NOT sort them, been there a very long time ago.

Taking into account the condition of the car etc, it ill be something very simple, BUT, it will take a little time to eliminate items as we go. DO NOT throw money and/or parts at it just yet, as that rarely solves anything, except the bank balance.

 

OK, as promised.

You have plugged the AAV inlet and dropped about 200rpm.

There is air somewhere, and the list does get loooong, and considering the car status as you mentioned, this what I suggest:

1) Remove the throttle cable from teh alloy capstan, thus eliminating it from cause.
2) Run the engine, and spray Ether, or even WD40 etc around the hoses at the TOP of the AAV, and the 2 on each end of the balance pipe across the rear of the engine.
3) Read the paper on HE Tune UP, and ensure the throttle discs are in fact closing as designed.
4) The Crankcase Breather system (as mentioned) can cause issues, and the easiest and quickest. is to cap the vac supply end of it, and observed the engines behaviour.
5) Your market has, sadly, a myriad of vac hoses under the RH aircleaner unit, and AGE is now seriously against them, and if they are perished and split, air is getting in.
6) At the rear of the RH inlet manifold are several vac hoses, one for the transmission, one for the heater system, one for the fuel load switch, another that is capped with a blanking cap Check them ALL, including that blanking cap for security and integrity.
7) Obtain a 1/2" (13mm) socket and bar and check all the inlet manifold nuts for security. It is well documented that the gasket/s settle with age and the manifolds come loose, and air is sucked in.
8), RARE, and I mean RARE, the brake booster diaphragm is split, old age again, and that will allow some SERIOUS errant air into the system. The vac pick up for that is on top of the rear end plate of the RH inlet manifold. Pull the hose, cap the nipple, and start her up and see if anything changes. DO NOT DRIVE WITH THAT HOSE UNPLUGGED, as you will have NO brakes, FACT.

If #1 sorts it, there ya go, and so on down the list.

I doubt it is overfueling, or you would certainly see, and smell the raw fuel.

I doubt it is anything complicated, the age etc you mention, negates that thought at the moment.

It is getting errant air from somewhere, and that is where I start with all the V12's I have sorted over way too many years.

If I remember something else, I will return.

PM me if you need some one on one advice, and walk through, but I maintain that the Forum is kept updated if we go that path, so when I am gone, the scribblings are still intact for others.

They, and systems that run them, are SIMPLE.

 

Bert,

Can you recall anything that might have happened when this issue started...any maintenance, any adjustments under the bonnet?

What was the idle RPM during the warm months?

Thanks,

John
1987 XJ-S V12

 

Grant thank you for all the help. I had typed a VERY lengthy response itemizing everything related to engine that i g\have done. Took a long time because i cannot type. THEN one of my BIG FAT FINGERS hit an unknown key, and POOF, its all gone!!!!! WHERE it went i have no clue and can't find it. I am too angry to even try and re-type it. Im sorry.

But to John i will say that the car drove PERFECT before it got cold here. In the summer it idles at 750. I plugged the hole in the air cleaner `TEMPORARILY and what changed now is the engine will START OFF at about 900 rpm and slowly within about 5 mins it will climb to 1500 instead of STATING UP COLD at 1500. I did do "Throttle Linkage Adjustment" and "Throttle Butterfly Valves Adjustment" as described in "Repair Operation Manual" (the big Green book) pg.337-338 earlier in the summer and drove the whole time without a problemI also did the "AuxilIary Air Valve Test" on pg.389 of same book. The AAV did not function properly when in boiling water. I spent some time cleaning it and "lubing" it and test another 4 or 5 times and the valve did close when hot and opened up again in cold water. Thank you again guys for trying to help me!

 

Something has failed in the period since the summer. You have an air leak, and it is a matter of finding it. You could try adjusting the butterflies completely closed (easy to do using the screw adjuster on each spindle); then blocking off the air to the AAV from the airbox; then starting the car. If it runs, then you should hear where the hiss of air is. My money, like Grant mentioned, is on one of the following:

• air into the manifolds from one of the spigots in each end, or
• into the manifolds from a fractured vac hose joining a spigot, or
• into the manifolds from a fractured balance pipe hose or a leaking ECU vac signal hose into the balance pipe, or
• check under A bank throttle body, there is a large diameter hose (about 1/2 inch) that joins here that is meant to supply vac to the cruise control bellows. You can feel for it but it is hard to see. This can easily become dislodged or can have cracks.
• or as has been mentioned, crank ventilation system leaking into the manifolds

Just a matter of patiently working through everything! Removing the airbox covers and the filters helps a great deal to see everything too.