Sorry for the repeat topic. I know this has been discussed before but I couldn't find it in the Search function.

I pulled an Aux. Air Valve off a parts car recently. Dropped it into a pot of boiling water that helped clean out the internal quite a bit but there is still more gunk in there. I don't have the equipment nor the desire to take it apart. Is there anything I shouldn't put in there to try to clean out the gunk and calcium build up? Thanks.

 

Calcium build up is a tough one.

Down here we have "CLR", at the Hardware store type outlets, but read the label carefuily, as some of this stuff is not good on alloy.

Some AAV have an alloy piston, some have a Stainless piston.

If yours is an Alloy piston, and has Calcium on the inside, I doubt anything will free it up.

 

Yep, we have CLR here to. I don't know if there is any way to tell it is an alloy or stainless piston. Hmmm.....The adjustment screw came out fine and cleaned up well. I used a wire brush and steel wool on the tubes as far as I could get in.

I remember someone saying something about when it is heated up in water you should be able to see the piston noticeably higher? and it retracts when cool. Or maybe I have that backwards.

 

Correct.

At operating temp the piston is fully UP, thus closing the port.

When cold, the piston is down, opening the same port for extra air that is required for cold start.

 

Soaked it in white vinegar all day. That took the crud off the spring. An old tooth brush got whatever didn't just rinse off. There is still some black coloring at the bottom of the piston holes. I am going to put it in some boiling water in a few minutes and see if I can get some movement from the piston. I'd sure like to have a spare that I know actually works.

Didn't get to do anything with the Jag today. Had to deal with a broken electrical wire on throttle control sensor on my Mustang. Took a while to diagnose the problem. Hopefully my temporary fix gets me to a where I can get a replacement connector tomorrow.

 

No luck with the AAR piston extending upwards when submerged in boiling water. Rats.

Looks like the AAR is nothing more than a fish hook weight at this point.

 

Put some penetrating oil on it. Bend a coat hanger ( wire ) to 90 degrees and cut then file the bent side as short as possible while leaving a good shoulder at the top. That should fit into the holes in the top of the piston. Or just buy some stainless picks. Pull that piston up and let it back down a lot. That will free it up but can't guarantee the bulb is still good.

If if it doesn't open in its own then rebuild it with Grants write up or toss it. It would make a terrible fishing weight.

 

When push comes to shove, and i think that is where we are at here.

Find a container, big enough for the AAV, fill it with Diesel Fuel, drop the AAV in it, replace the lid. Come back in a week.

If that dont free up all that Black Goo you have inside it, get a bottle of JD (for you obviously), and open the thing up and clean it out. Slurping as you go.

Takes me 30 minutes tops. First one took about 1 hour, and I was out of JD at the time.

 

Another option, acceptable to some but not others, is to do nothing and just live with an inoperative AAV. You wouldn't be the first, believe me. So long as is stuck in the closed position, that is. A week's pay says many V12 owners have a dead AAV and don't even know it.

I drove my XJS for years with a dead AAV and my present Series III V12 has a dead AAV as well. The only time it's missed is on exceptionally cold mornings...like near-freezing or lower.... when the engine might need a little help from the throttle for 30-60 seconds or so.

Cheers
DD

 

I got this AAV from one of the parts cars in the junk yard so its no harm no foul at this point. I don't know if the one on my car actually works or not but it's not at the top of my list of things to do. I've never had a problem with surging rpm's or cold starts so it may be fine. I just wanted one for a spare.

 

Doug:


That confirms what I was thinking of. But, I've no V12 experience, so I just watched.


Auxiliary air valve. Thermo sensed. Adds air upon firing up a cold engine. That part seems counter intuitive. Mixture gets leaner? Cold engines usually want a rich mix to fire up and run well.


So, a pure guess. The engine management adds extra fuel to a cold engine.


Therefore, the AAV adds air to increase engine speed. In olden days of carb'd engines, the fast idle cam.


So, on a car with a dud AAV, in closed, just add a bit of throttle on firing up.


As in ancient days, pre automatic chokes. Hand throttle under the steering wheel or on the dash.


What will I do with this extra knowledge, I've not the slightest!!!!


Carl

 

Carl,

With that knowledge you deserve a V12.

Well done, and precise diagnosis also. You would put many V12 owners to shame.

 

I have a 1991 xjs v12 and I believe my AAV is stuck open since I get a surging when in park or idle. Can I cap off this line and run the engine like that until I can either clean my old one or get a replacement?

 

You can, but it might mean the idle speed is so low the car will not tickover when warm. The airfeed to the AAV from the back of the B bank airbox also feeds the idle speed adjuster part of the AAV, this is the place to cap it off. If you look at my post above with details of my own solenoid mod, you will see a badly drawn diagram of the AAV/idle speed adjuster internals.
You would have to adjust the throttle butterflies to get a tickover if this is what happens. Mind you, it could be that the butterflies are open enough anyway, so try it and see.
Greg

 

Thanks Greg.

I placed a cap over the inlet in the B bank airbox the surging stopped and the rpm at idle is about 900 rpm. This is still a bit high but lower than it had been.
I thought I had a vacuum leak that was causing the higher than normal idle, but so far I have not been able to identify the cause. This problem has been going on for the past year or so.

 

At 900 with the AAV blocked, you do have a vac leak somewhere.

OR

The throttle disc adjustment has been fiddled with in an attempt to hide the prime issue.

OR

The inlet manifold/s are loose, very common. So take a 13mm (or 1/2"a/s) socket and tighten them up. Most go up about 1/2 turn, and that usually sorts all manner of havoc.

OR

The elbow on top of that AAV has a split on the underside, more common than most admit.

With that AAV blocked as you have done, I would expect 400rpm maybe.

 

Well I checked the elbow from the AAV to the manifold no issues, I tighten all the manifold nuts got maybe about half a turn on each. No joy with the idle still at around 900 rpms, however now I hear a slight tapping! Could this be a slight manifold leak or worse?

 

Norm
Stop worrying about odd noises. Now, make a cover for the throttle opening (eg a bit of flat wood with a WELL SECURED solid rubber face one side, bigger than the throttle butterfly hole, and hold it over first one throttle opening then the other as it ticks over. You should hear the engine note change and the revs fall very noticeably. If so, then adjust the butterflies and you will be OK until you decide what to do about the AAV/cold start. If the note does not change much, you have a leak somewhere.
greg

 

As per your instructions I covered each throttle opening one at a time and no change in rpm.

 

Therefore you have a decent sized leak! Nothing for it but to go carefully round each manifold, and each throttle body (NB underneath the TBs) and block off each and every entrance and see which one drops the revs.
Do not forget the short flexibles (tape round these flexibles to seal them) each end of the rear crosspipe, or the thin pipe across the middle of the V, or the flexible to the ECU in the middle of the rear crosspipe (very hard to get at, so do this one last).
Greg