This engine will only have a stable idle at 2000 rpm under two conditions: It’s cold, or it’s not really at idle, the throttle pot is telling the ECU that it’s above idle. In your case, I’d suggest that it just warmed up.
You have a manifold leak somewhere. Too much air is getting in at idle.
Jean,
To the contrary, you are very clever if you can do the things you have outlined. I will try to find photos of what I am referring to.
The injector seal is at the very bottom, well below the electrical connector and retainer plate. Oil will not hurt anything and should change the idle if leaking.
Yes, the 13mm idle screw is normal.
@ Kirbert : yes the engine was cold. I will try to find out where the leak is.
you are speaking about intake manifold I suppose.
@ Robert : I’ll try oil with injectors.
I really want to solve this problem, working on this car from more than 1 year 1/2 just to sort out all the little troubles that a prolonged 15-year shutdown created …
**
Idle should only be set with the engine hot, Jean - valid for any engine…
On the V12 the idle screw is integrated with the AAV, which, crudely, bypasses the idle screw. That said; the idle cycling is caused by too high idle; the ECO register that throttle is closed, cuts fuel - the engine slows and ECU resumes fueling. Engine revs up and the process is repeated - engine inertia makes for some rpm ‘overshoots’ beyond the nominal 1500 rpms cut-off.
However; in gear the idle should drop below the fuel cut-off rpms - does it? You have to hold the car on the brakes, of course…
In short; getting the idle down will solve the cyclic problem…
Engine rpms depends on the amount of air to the engine - more air increases rpms. The throttle switch only regulates fuel according to throttle settings; informing the ECU that more air is delivered - but the throttle switch(!) itself has no influence on air flow, which is regulated by actual throttle opening…
Methinks the 2000 rpms is excessive, and caused by more air delivered than the cold AAV can provide - ie; air is somehow delivered past the AAV in addition to the throttle gap correctly set.
An air leak is best approached with the engine hot. In idle the warm-up time is greatly prolonged, so the best idea is simply driving the car some 5 minutes - which should be adequate warm-up time, if thermostats are working correctly. There should be no problems driving the car; with the throttle out of idle, the fuel ‘cut-off’ function is not active. And if you have to stop the car, releasing the throttle; the engine may rev up, but if so in gear - hold car on the brakes…
Frank
xj6 85 Sov Europe (UK/NZ)
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Christophe,
AAV kit fron where?
Did you test it before you installed it?
As mentioned before, either the AAV is stuck open, you have a vacuum leak or your throttles are way open, mothing more and nothing else.
Bonne chance.
True, but the throttle switch does tell the ECU whether or not the throttle is at idle. If it’s at idle, revving too high will result in the cycling described. If the ECU thinks the engine is not at idle, it will not, it’ll happily rev to 2000 and stay there.
Offhand, though, I don’t think the throttle pot is the problem in this case. And whether it is or not, the first order of business is to figure out why too much air is getting into the engine with the throttle closed.
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Indeed so, Kirbert - the engine cannot rev without air…
…and I would not think that the AAV, idle bypass screw and correct throttle gap in any combination could raise the idle to 2000 rpms. However, a functioning AAV should be closed with the engine warmed up - and adjusting idle without the warmed up is pointless. So the engine should be run up to hot to verify AAV function - and/or the AAV/idle screw hose clamped, running the engine on throttle gap only, to pursue other leaks…
…which may be one or both of the overrun valves, easily tested…
Frank
xj6 85 Sov Europe (UK/NZ)
**
I finally removed the AAV from the car.
I did a test in my kitchen with hot water. I left the copper part of the AAV in hot water (simmering water in my pot on the stove) My thermometer read 75/78 ° C, but I felt my water was really hotter than that . Hope my thermometer is running well…(not sure)
The AAV never closed. I tried twice.
I feel like the opening has closed a bit, but I’m not sure. Everything was very hot and I had a little trouble holding it.
How long do I have to leave it in the water for it to close ? I held it for at least a good 1 minute and my hand was protected from the heat, but it was hot anyway!
If the AAV is stuck, what I have to do ? I used the repair kit from “John_John 1”. I followed his “rebuilt procedure”. The piston circulates easily in the AAV during assembly. I put the repair kit about 3/4 days ago…
but anyway, idling, even when cold, should not be unstable.
Some pictures :
I don’t have any hose clamp at the base of the rubber for ventilation crankshaft, it’s a problem ?
At the back of the A air filter box, it’s a hose coming from the AAV. I don’t have hose clamp here. It’s a problem ?
hoses at the back of the engine, from bank A to B :
the AAV :
Not sure about AAV, but turning screw (yes, with 13mm) should make a difference. Something sounds wrong.
If that proves to be working, i would take a quick look at PCV valve. Easy to pop out and plug with finger and see how much idle goes down. It provides a lot of vacuum at idle. It is normal for idle to drop about 400rpm with it plugged.
What and where is PCV valve ?
Jean,
It appears to me that the top of the AAV needs to be pressed into the housing further; the position is what limits how far the piston moves.
Google “Jaguar AAV rebuild” and there is an old article from the previous Jag Lovers site stating how to determine how far the top is pressed in, 70mm comes to mind, measured from the very top to the piston.
It should take less than a minute for the AAV to react to the bulb being submersed, and the temperature you state should close it completely.
So Robert, even with a cold engine, my idling problem may come from this part too far out ?
Look at what I received in the procedure about the top, no more info
Yes, it needs to look like the one on the right, with the red “x”.
And,yes, it will cause a very high idle.
This is a critical part of the test. The water needs to be bubbling, at least gently, which assures it’s at 100 deg C – unless you’re at high elevation. 75/78 won’t do.
Make sure the copper bulb isn’t touching the bottom of the pan. Other than that, you should immerse at least the entire bottom end of the AAV.
And it might not completely close, but it should nearly completely close.
Looking at your photos, I suspect that body needs to be pressed farther in – but not so far as the red X in the illustrations.
Kirby is correct again; I just looked at mine and it is perhaps .030” below the top of the body- definitely not above as the one with that Jean provided of his AAV. The one with the green check is from John John I think and might be ok. Mine idles at about 950 cold, and drops to 800 warm.
It does not require boiling temps to close when I tested mine, and idle on mine drops before the temperature gauge begins to move.
The measurement of 70mm at room temperature removes the guesswork.
Things are starting to be clear.
I will modify the position of the top of the AAV and I repeat the test with water.
It’s work for tomorrow.
Jean,
from what you write it seems issues are exaggerated by a fault of your thermometer. Not only 78°C is not enough, as Kirbert already remarked, but IMHO you would not be able to have “a little trouble holding it”, if it really was that temp. Make the water boil - bubbles don’ t lie! - and hold the part in a bar clamp to check - things should be a lot easier to assess then.
Good luck
Jochen
75 XJ6L 4.2 auto (UK spec)
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The AAV should start closing as soon as the coolant starts heats up, Jean, and gradually reducing air flow with increasing temp. There is little need for the AAV as the engine loosens up; and the AAV is not an ‘on/off’ switch. It is likely to be visibly closing at lower temp than your test, and nearly closed at that temp - and the idle screw takes over the idle rpms…
I may be out on limb here, but I cannot imagine the V12 needs to stay, and does, at ‘full cold’ idle until coolant is near boiling - but I’m willing to be corrected…
On the xj the the AAV was fitted with electric heating for rapid closing - reducing the high idle time, with no negative effects. The xj’s used a bimetallic strip, while the V12’s likely uses something like found on a thermostat (wax/mercury?), though probably quicker acting Thermostat is meant to control temperature and has a much narrower temp range…
Obviously, your AAV is malfunctioning for whatever reason - but the cyclic idle is related to excess air from whatever cause…
Frank
xj6 85 Sov Europe (UK/NZ)
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You’re not out on a limb, Frank.
On my XJS V12, years ago, the AAV died. And my present day V12 doesn’t even have an AAV. Lack of a fast-idle-when-cold hasn’t been a problem. The engine, even stone cold, will happily idle at 600 rpm.
Only when temps drop to freezing or lower does the engine need a bit of nursing with the throttle…and even then only for a few moments.
Cheers
DD
First cuppa coffee disclosure applies here.
Gentlemen, I don’t understand the recommendation for higher testing temperatures. I would expect the AAV to begin closing at something more like 50ºC and be closed at maybe 65-70ºC
What am I missing?
Cheers
DD
