Not sure what the previous owner did to the car.

I have it running pretty good now, except the when the engine is warmed up is around 1500 RPM in park.

It drops to, eh, maybe 900-1000 or so in drive.

Any ideas on where to start looking for adjustments he may have made? Is this possibly a simple throttle stop or linkage adjustment?

I think he may have made adjustments with old crap gas in the car, as i got the old gas drained/diluted/used up, the better the car ran and the faster the idle became

Thanks,
Doug

 

I wouldn't spend time chasing the PO, just get it set right. Set the throttle disks, the throttle linkages, the throttle position sensor, and you'll be most of the way there. Then check for air leaks. Once that's all done, the idle adjustment screw is on the side of the AAV.

 

AAV? Auxiliary Air Valve?

Is that the item in pic # 2 of post 6 and 7 in this thread?

https://www.jaguarforums.com/forum/x...le-tps-238279/

Doug

 

My money is on a sticking AAV. There used to be rebuild kits, but apparently they are not available anymore. It's an expensive part, but likely you'll have to replace it.

No, it's not the piece in the photo you mentioned. It's on the left side of the engine, on the water rail at the back. At the backiside of the left intake manifold there is a rubber hose that goes from the manifold to the AAV. There is a large bolt on the side of the AAV, that is the idle speed adjustment. Turn it in and see what happens. If it's already in, then the piston is stuck and you'll have to replace the AAV

Red arrow points to the AAV.

 

AAV rebuild kits are available. Great guy, great products.
https://www.ebay.com/itm/32460810686...mis&media=COPY

 

What's the idle like when cold? Does it rise or fall as the car warms up?

 

Idle RPM increases with temp increase. A few hundred RPM. I assumed the ~1200 RPM cold idle was just fast cold idle, as in most cars, but RPM rises to 1500-ish when the motor is warmed up, in Park.

No flux in the idle, either park or drive, just higher than it should be, but most noticeable in Park.

Doug

 

Classic signs of a stuck piston within the AAV. The car usually doesn't have the high idle that drops the way that modern EFI cars do, it varies less from hot to cold.

 

Hi, AZDoug! I had a similar issue with my 1987 V-12, and thanks to the help of all the forum members it was determined to be the AAV (although my symptoms were a rise to 1500, drop to nothing almost, repeat cycle). I had the AAV rebuilt in Lithuania by Jonas Loda. I think it cost about $172 with shipping. Excellent job, and worked like a charm! Jonas is on Ebay, listed as Jag Improver......
Warm regards,
John

 

John
FYI your up and down revving symptoms were caused by the car revving above 1400 rpm while the throttles (as told to the ECU by the TPS under the capstan) were shut.
This 'tells' the ECU that the car is on the over-run on a trailing throttle (such as drawing up to traffic lights) and under these circumstances the ECU cuts the fuel injectors to save fuel until the revs fall below 1400, whereupon it starts up the fuel injectors again. And on like this in an unending loop at tickover until the AAV is fixed!
On Grant's advice, I fitted a solenoid actuated, cabin switched extra air device as I got fed up with the AAV being a problem when I stopped using the car every day. They tend to jam with less use, I found. Maybe the ebay guy fixes them better than new!

AZ Doug's one is obviously staying just below the 1400 rpm mark, which is why his revs are not cycling up and down.

 

I looked and mine valve doesn't look terribly difficult to remove, relatively speaking compared to other parts. But not as accessible as the one shown in the pic above.

Biggest issue i see is the rock hard rubber hoses which will have to be cut for valve removal.

Are those connector hoses generic size that can be obtained at a local auto parts store?

I saw it was said it is attached to the water rail, does that mean the the coolant will drain out when i remove the valve? Or is it a dry connection? I see a gasket under the valve.

Does the vlave just respond to manifold vacuum changes?

I am sure I can rebuild it without buying any parts, i have a mill and lathe, I can work from there. As long as the spring is OK.

Thanks,
Doug

 

I was able to match up some hoses by cutting portions out of various radiator hoses. I can't remember what they came from.

There is no vacuum involved. Yes, coolant will come out when you remove the valve. It's basically a thermostat, the wax bulb expands as it heats and pushes a piston upward to close off the air inlet port thus reducing the idle speed. Over time, the wax capsules wear out and they don't expand as much as when new, which gives less movement of the piston. That doesn't cut off the air as it should, and you'll run out of adjustment on the speed trimming bolt.

The top hat portion of the valve needs to be removed to access the piston, and the hat was a tight press fit when new. You'll destroy the wax capsule when you take the valve apart. I'm sure there are photos either here or on Jag-lovers of a valve being rebuilt, don't cheap out and try and reuse the old wax capsule if it's original to the car.

I too have a lathe and a mill, they won't help for getting the valve apart.

 

OK, didn't know about the wax motor.

I guess the rebuild kit is in order.

Doug

 

Hi AZDoug

What you have to be Careful of, is that you don't Snap the Bolts when Removing the AAV as the chances are that they have maybe Corroded themselves in and if you happen to break the Bolt

Then you could be left with a Problem, much bigger than the one you Started with!

It is entirely up to you but knowing this can happen, these were Dice I didn't want to Roll, so I came up with a Fix that Cost me Nothing and Did Not Involve me either Removing or Adjusting the AAV

Instead what I did was to insert a Metal Tube inside the Rubber Tube to the AAV to Restrict the Airflow to the AAV as before I did that my V12 Engine was Starting up in Park at over 1500 RPM

So when you put the Car in Gear, there would be a very loud 'CLONK' from the Gearbox 'And you Don't Want That!

What Size Re-stricter Tube you use, is a matter of Trial and Error, although it should be a very good fit in the Rubber Tube you push it into

It did take me a Couple of goes to get the actual Hole in the Restriction Tube the Right Size

But now She Starts at 800 RPM and Stays like that, even when the Engine has Warmed up

I didn't even have a Lathe to Bore out the Restriction Tube the Right Size but Since you have 'You Should be Laughing Sand Bags!'

Hope This Helps

Alex

Restriction Tube Hack to Prevent the Engine from Hunting or Revving Up and Down
Page: 135 on my Cherry Blossom Restoration Thread

 

Actually, something along those lines occurred to me also. Except i was thinking of a restriction tube with en external adjustment, basically a bolt you turn in or out. Stainless sleeve, bolt and locknut. I did something like that for water flow control on a different vehicle, many years ago.

Thanks!

Doug

 

Hi AZDoug

At first I was thinking of doing the Same by using an adjustable Tap instead of using a Restrictor Tube

But then I changed my mind, as once you've got the Rev's right its not something that you want to keep 'faffing' around with

She always Starts at 800 RPM and always stays at 800 RPM even when held up in a queue of Traffic on a boiling hot day

Whereas on a Freezing Cold day, then I might have to 'Feather' the Throttle just a bit until the Engine Warms up to prevent her from Stalling which has so far never happened

Its up to you but I would keep it Simple

Alex

 

Any recollection on what the restrictor tube inside diameter was? Its a starting point.

Thanks,
Doug

 

AZDoug

I used a piece of 13mm Copper Water Pipe Tubing, that got the Revs down to about 1000 RPM

But you are really looking for 750-800 RPM so you probably want 11-12mm then you can always Bore it out a bit more if you need to

Alex