An engine needs extra air when starting from cold, partly to overcome the increased friction of cold oil compared to hot. That extra air needs to be fed into all cylinders equally, and Jaguar chose to use a single metering device ( a good thing, otherwise synchronizing two metering valves would be difficult) plus the balance pipe. They needed the balance pipe because they used two completely independent manifolds, one for each bank.

Typical V engines, such as V8's and V6's have the intake manifold and throttle assembly in the V, so it's easy to have the air fed to all cylinders. The V12 didn't lend itself to that, partly because of the decision to put the spark plugs and distributor in the V, so the AAV and balance pipe performs the same function.

It depends on the conditions, but I can say from experience in very cold weather a V12 with an AAV that is stuck closed will not start unless the throttle is opened slightly.

 

jagboi 100% right. In cold weather the V12 HE will not tickover after starting, either, unless it has some sort of extra air device. The AAV works well, but not for ever. When my car was my daily driver the AAV worked fine for nearly 10 years.
Now, I have incorporated a cabin-switched solenoid extra air valve from the Jaguar AJ6 3.6 engine, as with less use of the car, it is a better solution.

 

Well......how cold is "cold"?

At least down to near-freezing mine works fine without an AAV. Start 'er up and she idles just fine. Drop it gear and drive away. If freezing or lower a few seconds of gentle revving needed before she'll idle easily.

Cheers
DD

 

The only time I tried it, was -20C. The car usually stayed in a heated garage but that night it sat outside at a hotel. Next month with a working AAV it started fine in -25C, so I'm blaiming the AAV.

 

Just thinking about it quickly.

Is it really just a matter of blanking off what needs blanking off to 'cut' the AAV out of the system??? I've been driving more, summer, and having the extra revs for the first 4-5 min of driving isn't needed, and a bit annoying. Nothing bad, terrible by any stretch of the imagination, but unneeded. And,,,

Thanks to global warming, lol, it rarely gets that cold here. Me and the lady are thinking about a permanent move to VT or Upstate NY,,, where a little gentle coaxing of the gas peddle might be necessary,,,, but it would be a cold day in hell before I took the red ol lady out in the dead of winter on salty roads... Really, if it's not a crazy maker I could try this today. My AAV elbow is fairly new so I'm not too worried about it cracking when I pull it oft... Just the vac air thru the dizzy, but I have some open air spots thanks to removing the carbon canister...

Easy work? Or complicated?

How does one NOT lose the use of the idle control screw/bolt? In eliminating the AAV?

 

The theory is sound - simply stop it letting air in - you'll find out pretty quick if its busted because your idle will turn to **** and need sorting.

The second they're out with salt here the XJS is grounded for me also, that said I'll still be running it on a weekly basis / bi weekly but it won't pass the gate until at least a month after the gritters go home.

 

JJJ
Take a look at this to see how the AAV can be modified yet keep the tickover adjuster:

 

Got it! This is the thing!
Thank you, Greg!!!

 

I've done a couple of sets of cam covers like this for friends. I like the contrasting colors.

 

I think I'd rather have it fitted to a car than over my desk on a plinth.

I think these would look real nice in black but with the top part and the fins diamond cut, then lacquer the whole thing.

I don't think I'll DIY this aspect of my motor, this is a ways down the road, got to get it back on the road first, need to get the cobwebs blown out of it after 17 years asleep. Dropping the sumps and doing oils, possibly brake pipes this weekend, cooling system next weekend.