Hi there!
I finally got around to getting my '90 XJ-S running again a few days ago. That entailed replacing the fuel filter, spark plugs, plug wires, rotor and dist. cap. It had been sitting for several years.
Upon starting the engine, it immediately raced up to 2000 RPM and stayed there. Probably not real good for engine life. 
I shut it off right away. The friend who was helping me on this project and I agreed we probably had a significant vacumn leak somewhere.
While I was away, my friend found several suspects in the vacumn leak department and fixed them. He then started the car and told me later that it idled just fine. Life is good! However, when I went out and started the car the next day the engine raced right up to 2000 RPM again and stayed there.
If my friend says the car idled properly when he started it, I believe him.
Any thoughts?
Michael
Michael,
It sounds like it could be a problem with the Extra Air Valve (EAV) also called the Auxiliary Air Valve (AAV) located at the rear of the left side intake manifold. The EAV has a piston inside that slides up and down based on coolant temperature allowing more air into the engine when the engine is cold and then slowly closing up as the coolant temperature increases. If the piston inside the EAV/AAV gets stuck it could cause the problem that you are seeing. If you haven’t already done so, download Kirby Palm’s “Experience in a Book” from Jag-Lovers and read up on it. You may have to remove it and lubricate/exercise the piston to get it to move properly and then reinstall it to verify that. It is quite possible that this will fix your problem. I have removed them from my V12 engines in the past and tested them on our kitchen stove to see if they worked properly.
Regards,
Paul M. Novak
1990 Series III V12 Vanden Plas
1990 XJ-S Classic Collection convertible
1987 XJ6 Vanden Plas
1984 XJ6 Vanden Plas
1969 E-Type FHC
1957 MK VIII Saloon
Ramona, CA USA
Thank you, Paul!
I do have Kirby’s book and will follow your advice.
Thanks again!
Michael
Hi there!
After reading the section in Kirby’s book about the idle adjustment screw (or bolt!) and the AAV, I blocked off the opening in the air cleaner that both use to meter air into the engine. The idle dropped from 2000 RPM to 700 in neutral and 500 in gear.
At first I was well pleased. Then I realized I was blocking the idle screw circuit as well as the AAV and this didn’t seem like a perfect solution. Then I went to the archives and found a fairly intense thread in which Kirby made it clear that he felt, under the same circumstances I was experiencing, that the problem was not with the AAV but with vacumn leaks elsewhere in the engine.
I just got through driving the car down town to fill up the gas tank (ever the optimist!) and it drove sweeter than it ever has since I owned it. It has been sitting for almost five years, so I have a bunch of work to do to get it road worthy. I am willing to put off tackling the AAV/vacumn leaks issue until I have brought the rest of the systems (hoses, belts, fuel lines, brake lines,etc.) up to speed. Will I be doing the car any harm if I pursue this line of attack?
Thank you for your insight!
Michael
Hi Michael,
You “blocked off the opening in the air cleaner” and the idle speed dropped dramatically.Basically, you starved the AAV of its air supply, causing your idle speed to fall. I think that is exactly what Kirby stated in his Book. The engine gets enough air from other sources to run at idle, the distributor vent system for one. PCV for another. Throttle plates also. You could jam a cork in the opening you blocked off, and do no harm, until you fix the AAV properly!
The 2000rpm fast idle speed, though, has to be coming from other places, as well as the AAV, IMHO!
Hi Dave!
Thank you for your response!
I’ve decided to try to resolve the vacumn leak issue before putting in any more time and money into the car. So here are a few more questions.
I didn’t have a Marelli distributor cap gasket handy when I installed the new cap. Would that lack be a possible source of a vacumn leak?
Up towards the front of the right hand side air cleaner there is a small, cylindrical shaped gizmo attached to the engine by several hoses. There is a small hole in the air cleaner that seems to be a perfect fit for the gizmo. A perfect fit if the rubber grommet that would locate the gizmo in the hole were present. Currently, the gizmo is laying there unattached and the hole is open. Could this be a vacumn leak source?
What is the gizmo’s function?
Any hints on how to replace the grommet.? My current plan is to go down to the local parts house and buy a selection of grommets that MIGHT fit and hope I get lucky.
Thanks to all of you for your very helpful advice.
Michael
When I replied to your previous post, I didn’t notice the year of your car with the Marelli ignition. I assumed (wrongly) that we were working on a Lucas equipped ignition system. That is what I have on my car. If the Marelli cap has a vacuum hose connected to it, and a vent system, then the lack of a gasket will result in poor airflow through the distributor, and entry of dirt, that’s all. Paul is better qualified than I am with Marelli cars! The “gizmo” sounds like it may be the supplementary air valve, which should have an electrical hookup, and a vacuum connection, too. If everything is connected as designed, the gizmo is supposed to boost the idle speed when the A/C compressor is on, thus slowing your idle speed. Clear?! The open hole in the “A” bank air cleaner rear housing is letting dirty air into your engine, but not a vacuum leak. I know you can replace the grommet with no difficulty! Read the “Marelli” section in The Book, too!
Dramatically – but not enough. When you plug that opening, the idle should
drop to somewhere around 200-300 rpm. If it’s higher than that, there are
vacuum leaks elsewhere that need to be addressed. The fact that it fell as
far as it did, though, tells me the AAV itself is also a gaping leak.
I should point out that one of the non-AAV leaks may be the butterflies.
They can be adjusted incorrectly, or they could be sticking open a bit. If
sticking, sometimes the idle is inconsistent; if you’re at half throttle and
completely get off the pedal it might go to a slower idle, but if you very
gradually reduce throttle to idle it might stick and stay fast.
Also, if you cover the intake openings to both air filter housings, the engine
should completely stop. If it’s still running, the air is coming from a leak, and
you probably can hear it. If it stops like it should, though, it probably
indicates that the problem is in the butterflies.
I have long recommended disconnecting the distributor vent system from the
AAV inlet elbow and connecting it directly and independently to the inboard
side of the air filter housing. One reason is because the little plastic fitting
involved in connecting it to the AAV inlet elbow tends to crumble, but another
is that it makes analysis so much easier. Once that system is separate, you
can plug off that AAV inlet and there will be NO air getting through it. You’ll
know exactly the extent of non-AAV vacuum leaks you have.
– Kirbert
That is the Supplemental Air Valve, or SAV. It’s supposed to boost idle
when the car is warming up and the timing is retarded to light off the cats. In
later cars, it’s also used to boost the idle when the A/C compressor is
engaged if the car is in gear. There’s a pair of relays on the radiator top
rail to control that function.
The opening to the air cleaner being open is bad because it lets unfiltered air
into the engine, which is bad but it’s not the problem you’re looking for. If the
OTHER end is disconnected or the SAV itself is jammed open, yes, that’d
boost your idle! Note that the SAV itself is actually an electrically-operated
heater control valve from some other model of car, it was designed to control
coolant rather than air. It tends to get rusty and jam.
Here’s what I did to fix my SAV:
http://www.jag-lovers.org/xj-s/book/SAV.html
– Kirbert
If the Marelli cap has a vacuum hose connected to it, and a vent
system…
Note: The Marelli has the same vent scheme as the Lucas, but in the Marelli
both vent connections are in the distributor body, not the cap.
then the lack of a gasket will result in poor airflow through
the distributor, and entry of dirt, that’s all.
I don’t recall the Lucas ever having a cap gasket! I don’t think it’s a big deal,
but you do need to be careful that the clearance between the rotor and the
cap is correct and nothing is interfering.
– Kirbert
Hi.
After mine sat for a while it did the big rev thing in idle. I fiddled with the AAV for yonks without luck. Mine turned out to be the PCV valve. I figured it out using a piece of cardboard (about A4). Whist it was revving I felt I could hear a hiss some where in the roar. So by holding the cardboard over the motor and moved it backwards and forwards I stopped at a point where the hiss seemed least (the cardboard blocked it) which happened to be over the PCV valve. I disconnected it’s hose and put my finger over it and the revs dropped to normal. Worth a try and if it is the PCV valve replace it…cheap as chips, don’t try to clean it.
Trev
my usual way of tracking down a vacuum leak is to stick a piece of fuel line in my ear and move the other end around anywhere that I might suspect. I found hissing from my injector seals that would not of been found with other methods. another trick I use is to disconnect a vacuum hose and blow smoke threw it. engine not running and block of the throttle bodies and dist. to contain the smoke. this is quite the feat on a v-12 but with a helper to hold rags over throttle bodies and enough smoke/pressure, it will exit at any available leak.
You can try the old method of spraying carb cleaner wherever you suspect a vacuum leak. Or, if you have a propane torch, remove the nozzle, put on a piece of rubber tubing, and into the tubing put a short piece of metal tubing the the output end peened down to a small opening. Start the car, turn on the propane, and move the tubing to suspected areas. If the nozzle is fine enough, you can pinpoint the location.
Don’t forget the intake manifold gaskets as a possible culprit.
Hi there!
I found the vacumn leak! The hose to the Supplementary Air Valve was cracked in several places. Once I replaced it she purred like a cat. By the way, the device I used to plug the AAV opening in the air cleaner was the cork from a bottle of Barefoot Proseco. Proseco is a champagne style bubbly from Italy. The cork stem fit snugly into the oriface of the air cleaner and the mushroom head of the cork insured that it wouldn’t get sucked into the engine.
I can’t thank you guys enough for the time and energy you devoted to helping me out. I really do appreciate it and I do not take it for granted!
Now it’s on to a coolant leak. It appears to be coming from the bottom of the coolant reservoir tank that mounts on the front, left firewall. Once more into the breach!
Michael