High Idle Speed and Lack of Engine Braking
 

Hello fellow Jag lovers! I have read several older postings on the subject of idle problems, but I want to revisit to see what you experienced folks have to say about my issue. My idle in park is about 1100 rpm, but when driving, the car basically goes along by itself i.e. in urban areas, there is hardly a need to press on the accelerator! I need to slow things down a bit, say to the 750 rpm target at idle, in park. So, here are my questions:
1) I have checked the butterfly throttle valve and it appears to be at 0 rather than 0.002 inches, which I believe to be the spec. This should give lower idle speed, at the expense of a richer mix (high gas consumption), correct? If I move the valve to 0.002, will the idle speed not increase?
The car uses lots of gas right now, and the tail pipes are black and sooty, suggesting to me a rich mixture.
2) If I go to 0.002 for item #1, I then plan to look at the aux. air valve (AAV). Today, I adjusted the idle bolt, and there was little to no change in idle speed. I am thinking the AAR is seized? Thoughts?
3) I have looked for vacuum leaks. I noted that the carbon canister is missing on this car, and the vacuum line that did go to it simply has a bolt screwed into the end. The other end is just lying near the left front manifold.
The larger connection on the carbon canister is just tied in place, and there is a valve or something on this line.....not sure what it is doing. The other end of this purge line goes to a connection at each manifold. When I block the end of the line, with engine running, there is no change in idle speed, suggesting that the item noted above must be a check valve to something? Thoughts?
4) I have another vacuum line near the left manifold and it has what appears to be an inline fuel filter at the end; the other end disappears in the area of the distributor. I cannot see where this goes but again, no change in idle speed when I plug the line with the engine running.

I believe that's it for my questions on this high speed idle problem. Any and all feedback will be appreciated.
Regards,
Wayne

Wayne is the car a XJ-40 body style or a Series 3 body style V12 which was made until 1992 ?

Just on GP:

Clean the throttle bores and reset the throttle butterflies to the correct .002"

Yes, the idle speed *should* increase. If it doesn't it means a greater amount of air is entering from elsewhere




That's not the best indicator, as even with proper mixture the pipes will be black


Quite possible, even likely.

With some pliers squeeze down the rubber hose that runs from the backside of the LH air filter housing to the AAV. Does the idle speed drop?


If the canister is isolated and the main vacuum metal/rubber pipe that goes to it is blocked off, you should be OK...as least as far as idle speed is concerned. Why is it been defeated is curious. It's a little complex...I suspect someone got frustrated


It's the filter for the inlet of the distributor venting system. It should very slight vacuum but, in any case, it is *ahead* of the AAV so it wouldn't cause your high idle



Probably a stuck AAV and someone closed down the throttles trying to fix the high idle

Cheers
DD

It is the Series 3 body style V12. The model is a V12 Vanden Plas.




__________________

I tested the aux air valve today, in the pot of boiling water, per the service manual. The valve was open when I started i.e. it would allow air to pass thru. When I put the bulb sensor in the boiling water, the valve did not move. So, looks like the AAV is at least a part of my problem.
Can these units be disassembled and cleaned up to put back in service, or is it best to just order a new one? I have not tried to disassemble yet but I guess I have nothing to lose by doing so as it does not work anyway. Comments?

Yes, they can be rebuilt.

Attached is a write-up on the repair procedure. If you can't open it (I can't...some sort of glitch?) just search the archives with "Grant" and "AAV rebuild" and it's bound to pop up.

If you're a JCNA member then look thru back issues of Jag Journal from a year or two ago. There was a great pictorial how-to. As I recall Grant authored the article

There's a guy on Ebay selling his "AAV Rebuild Service" as well

Cheers
DD

Here's the JCNA article

Jaguar Journal July/August 2015

Cheers
DD

Thank you Doug for the guidance; I was able to open the attachments and the write-up was excellent! I immediately went to work and took my AAV apart. It was well gummed up and seized in place. I cleaned it up and the bits looked good; had good smooth action on the piston. Assembled everything and tested it, but, still no movement. Took it apart again and applied the heat from my propane torch, and I note that the part that is supposed to push on the piston does not even move. I am now thinking that I have a faulty heat bulb on the AAV. Does this sound correct, and/or, have you seen this problem before?

Wayne: trying to resurrect the AAV is a real chore. You will be better off getting a new unit - if you cannot find one for the late 5.3 engine (that, mid 80s onwards) you can use the unit which was specified for the earlier V12 cars. It looks a bit different but is interchangeable.
And that small filter on an air line is not vacuum - it is attached to the distributor cap and functions as a safety vent.
The V12 will happily idle smoothly as low as 500 rpm.
Check the vacuum line that runs from the rear of the cross-over pipe at the back of the engine to the ECU in the trunk. If this is loose at either end your fuel consumption will suffer significantly and it might also affect the idle. The carbon canister connections should not affect the idle at all. And that check valve is from one of the lines going to the canister. The design of the canister, that is the configuration of the connections, changed from time to time on the V12 cars.
You do know that the one frequent failure point on the V12 is the module in the ignition amplifier? The part is a GM part (Delco 1906), easily available. You should carry a spare. The first sign of a failing module is difficult warm/hot starts.
In 1988 there were only about 400 of the V12 VDP cars made ( I have the exact figure somewhere) . What colour is it?

Thank you "sov211" for your very informative response......all good info and I am sure it will be helpful to me as I work my way along with this car to try and get it running smoothly, and to give me some confidence in taking it some distance from home!
As for the AAV, I was rather disappointed today after I cleaned and re-assembled! I had nice smooth movement with the piston, but unfortunately, no push at all from the heat bulb! So, I guess I have no choice but to look for a replacement, or order a new one! I see they are rather expensive units! Thanks you again for your helpful response!
Regards,
Wayne

One question to add! Is elimination of the AAV an option? I recognize this would result in poor warm up with a cold engine, and potential stalling until the engine is up to temperature. However, this will be a good weather driver and I do not expect to ever be driving it in really cold weather conditions. Thoughts?
Regards,
Wayne

A dead bulb is common.

I used a bulb from a very low rated thermostat....125ºF as I recall. These low temp thermostats seem to be common at marine supply outfits. I might be able to find a part number.

Cheers
DD

Elimination is not unheard of at all. And many AAVs are stuck in the 'hot idle' mode and the owners seem to get by....in some cases probably not even knowing there is 'supposed' to be a high idle. As Gregory mentions the V12 will tolerate very low idle speeds.

I had a dead AAV, years ago, on my XJS. The lack of high idle in the morning wasn't an issue until sub-freezing days set in. Even then it's just a matter of manually holding the throttle open a wee bit for 15-20 seconds to prevent stall out.

Cheers
DD

If you remove the AAV, though, you'll need another source for the distributor vent. I rigged up a alternator on a pal's V12 by using JB Weld to affix hose nipple to the backside of the air filter housing.

Cheers
DD

Thank you Doug and if you do have a part number for the alternate bulb replacement, that would be great. I have not yet taken the bulb out; I am assuming it is just a press fit into the body of the AAV?
Re that distributor vent which ties in to the air supply line to the AAV, is it really a vent, or might it be vacuum advance to the distributor? I have not yet gotten in to explore the distributor area; it looks quite busy with all the plug wires, fuel rails, cruise bellows, etc etc!

Will look for part number

The hose is indeed a distributor vent.

If you look where the diagonal engine bay brace meets the LH fender you should see a hose with a small filter attached. That's the other side of the vent system; the air inlet side.

Look at items 11, 12, and 13 here:

Distributor-5.3 Litre - Parts For Series III Saloon | Jaguar Classic Parts UK

Cheers
DD

Plus one for the AAV elimination, I simply found an item (South African 1 cent coin) that fits snugly into the mouth of the AAV, ie before the piston, and sealed it off with some sealant, if you push it right down the mouth, you'll notice you still have the idle venturi open, so idle speed can still be adjusted in the usual manner.

Thank you Doug and Nathan for your input and suggestions. What I have done is eliminate the AAV functionality, for now anyway. Longer term, I expect I will want to re-work this and re-establish correct function, but for now, I am hoping this will get me back on the road. So, here is what I have done:
I cleaned up the AAV and got the piston working smoothly, and then re-assembled with lots of Never-Seize, but, I did not put the spring back in place. Rather, I put a small wooden spacer that maintains the piston in a closed position, to replicate the way it is supposed to be when the engine is hot. Then I re-installed the AAV. So, Nathan, I believe this will be the same in operation as what you have done with the South African coin! i.e. the idle adjustment for a warm engine should still work, but no fast idle potential during warm up. And Doug, I still should have the vent function for the distributor! Have I missed anything or do you think this should work OK? I will be testing tomorrow as I wanted to let my gasket sealant cure overnight; also, I simply used silicon sealant on the housing sawcut as I expect to be taking the unit apart at some point in the future to get the heat bulb replaced, which would get me back to original functionality (just have to remove the wooden spacer). So Doug, no panic, but if you do find the part number for the heat bulb, that will be appreciated.
I will post tomorrow to let you know how things go when I try to start her up with this AAV arrangement. Thank you again for your help!

Doug, thank you for the clarification on the distributor venting system. I feel better now in that I know what that open ended filter is at the left fender, plus, I know that it has a discharge end at the AAV supply pipe. I have one other small rubber line that currently lies open ended at the left air cleaner/fender location, which I will follow tomorrow. It was near the distributor input line filter so I was thinking they should be connected, but they did not fit! I am now thinking there may be a connection under the air cleaner where this hose should be going? Will explore further tomorrow! Thanks again!
Regards,
Wayne

That AAV set up should work perfectly, you'll probably just get a drop of about 150 rpm from cold to warm, then again that depends on ambient temperature.

Your rubber line under the left air-cleaner has me puzzled, I can only think of a fuel regulator line... Perhaps try tracing at back and see where it leads to.