I purchased last spring a 1986 XJ12 (VDP). Such a beautiful car!

It was not running but i got it for quite a low price.

There were a few known or possible issues: fuel pump, alternator, battery....

I started with the fuel pump. I 'got' it running by using the power antenna positive from the trunk. I had a great surprise to see the car did start however it was running poorly. It sounded like it was missing a few cylinders.

I flushed the old fuel and replaced with fresh one with additive for winter.

This spring I changed all 12 plugs, wires, cap and rotors.

The car start great every time and stabilize at 800-900 rpm. When I rev it, it smooshes nicely...I am not sure how to say it, maybe it is the 12 cyl but it is a very quiet engine that just go in the rpm so easily and with a great sound!....

....for a few minutes. Then the idle goes down gradually....and finally the car stalls. I can restart the car but it does not hold the idle. it runs good when i accelerate but stalls again as soon as i let go.

the engine does not really have time to warm up a lot so, especially here in Canada, it is not overheating, it is not even warm. but if i leave it for 1/2 hour then it restart no problem.

any advice? is there some cold injector in the 1986 XJ12? I thought that it could be but I cannot find them.
coolant sensor maybe?
fuel pump?

Thank you for any advice or guidance.

 

Welcome aboard.

The first item I would change is the Coolant Temp Sensor (CTS), located on the rear section of the LH thermostat housing. They are well documented as a flaky item as age creeps in. This CTS is the PRIME sensor for fueling.

Also check the wiring inside the plug and the rubber boot very carefully, as again, old age is at play here.

The Throttle Position Sensor (TPS) located under the central capstan at the rear of the engine is also an age related failure item now, BUT, the nice steady rise you have in the rev range is usually non-existant, so maybe it is OK.

The throttle bodies, one each side, get caked internally by "black goo", and this will reek havoc with idle. Simply wipe them out with a solvent soaked rag at each oil change keeps things all warm and fuzzy.
uxillary Air Valve (AAV), located at the rear of the LH cylinder head is highly suspect. The 13mm hex head hanging out the side is the "idle speed adjuster", and is used to adjust the HOT engine idle, BUT, if this valve is jammed, and they do jam regularly, the cold idle will be TOO SLOW, and that engine wil stall. Unscrew it about 2 turns, NOTING WHERE YOU STARTED, and see if the issue you got change at all. I really do suspect that AAV is jammed.

Your market possibly does NOT have cold start injectors. Jaguar played with/without them throughout the XJ-S life. I remove them always.

Have a read of the attached Doco's I have written, they may help.

AAV rebuild procedure.doc

Adjusting the ECU fuel pot.doc

HE Tune up.doc

SETTING THE THROTTLE CAPSTAN AND RODS GRANT.doc
The A

 

thank you very much for the quick advice and all the good suggestions.

that will keep me busy for a few weekends.

I have a few more questions:

coolant: is the (expensive) jaguar stuff the only one to use or is prestone or other multi-use ok? The head gasket seems to be a weak point, like on the old BMW, and that is generally linked to poor maintenance or neglected coolant. If I change the coolant sensor, I might as well take care of the coolant.

for Ontario or web users, is there a good place where I can buy GOOD Jaguar parts, other than the dealer? I am sure that some parts are only at the dealer but others parts could be sourced on-line or to other resellers.
I found the plugs and wires at Platinum Auto, a great place for parts, for just less than $ 120.

But the cap and rotor, I got at the dealer.....for $ 240.

I have a Jaguar and I am ready to put some money in it but at the same time, I prefer to do it right and wisely.

 

My opinion from waaaaay down here.

Look at the Vendors that support this forum.

I have used XK Unlimited in San Louis Obispo for a long time with no issues.

The CTS is a simple Bosch unit, same as some BMW, Merc, Volvo, and Aussie cars. The Bosch part number I remember ends in ..........023, and has a Blue top to it, where the original unit has a White top.

The TPS is JAguar unique, but teh online has it readily available.

Most other service items are Generic, and quality is not a real issue for me.

Always remember that Jaguar (and most other car makers) actually DO NOT make their own specific items, they are made by the "brand boys", as in Bosch, Lucas, Delco, etc etc, and do fit other cars in most cases. Finding what does what, is the cause of the "Grey hair" we older Jag owners have.

Your market dictates what is available, and brand names we have/use down here, mean absolutely nothing to your suppliers.

 

Forgot, I do that sometimes.

The coolant, oh my, nothing special.

A good quality "Long Life" coolant is all it needs.

The "open deck" engine is the enemy of the head gaskets more than anything else, and as I said before, head gasket failure into the actual combustion chamber is rare UNLESS that earlier "fool" overhated the engine.

Our S2 V12 (Sir Arthur in my garage) has now gone way past 500000kms, and the engine is as Jaguar assembled it. Most of the bits on the outside have been attended to over the years.

 

time for an update!

i continue with my tune-up and changed the 2 air filter. it was a good time to see more behind them and clean at the same time. so one more good thing done!

i followed the advice and started with item #1: coolant sensor temperature. I removed the old one quite easily then it fell apart in 2 pieces. those things happened!

the new one seems to be working much better...or something else that i may have touched! the car keep the idle very nicely now.....it does not stall anymore after 1 minute. i was able to take it for a short drive.

so first, a big thank you to Grant Francis. I wonder how many Jaguar are alive out there due to your advice, but add one to the count.

in fact the idle may be running now....too high! it is not that warm here in Toronto so with the car idle for 10 minutes, it sits at 60C, which seems well controlled. I am new to these cars but the engine bay seem warm...i hope that the temperature gauge does work. It seems to be as it start cold and move up after several minutes then stay nice at 55-60C.

no leak nowhere, no smoke, just a nice purring....but generally at 1000 or slightly above, like 1200 rpm......isn't it a bit high for a warm idle?

this weekend, I will look at a few electrical items (lights and mirror) then I am hoping to be able to take it for a 50 km ride on the road. The car has sat for a few years and iam sure that it will do it good to go out for a while!

once again, thank you Grant! I am hoping to post a few pictures of 'mylady' this weekend also.....

 

Always good to hear a plan come together.

The HOT idle is too high.

Down the rear of the B Bank (LH side) you will see an alloy valve thing sitting vertical on the cylinder head. Poking out of the side of this valve is a 13mm hex head of what looks like a bolt. This is the HOT idle adjusting screw. Turn it IN to lower the HOT idle, and OUT to raise the HOT idle.

That valve is called teh AAV, and is made by Lucas, and is a PITA on any day. Rebuilding them is simple.

I have attached my write up on that very subject for you.

AAV rebuild procedure.doc