Hi All,

Yesterday I picked up a 1992 XJS V12, gorgeous car, but, a basket case at the same time. I've been a fan of these ever since I was a kid. So I pulled the trigger (got a good price) and my goal is to start a thread documenting the process of fixing all the known and unknown problems

This one did come up locally as a "mechanics special" LOL and it was priced low... turned out the body/paint/interior is in very good shape, but the car does have quite a few moderate mechanical problems. It runs quite well but, here are the major issues:

- Erratic Idle - bounces like crazy when starting.
- Exhaust leak somewhere (between the idle and exhaust leak it won't pass CA smog)
- In board rear brakes leak really badly - has no stopping power at all! Scary stuff. Probably needs a full replacement.
- Power steering fluid leak from a lower hose somewhere...
- Something keeps discharging the battery.
- Steering is very loose and vague (a knock can be heard from from the front when going over moderate bumps).

Other than that there are minor cosmetic issues, but, when the car is running WOW, the V12 is super smooth and sounds great! This car is worth saving - the previous owner just let it sit for the last year after the brakes went out but he did take good care of the car up until then. Its got about 78k miles on it and good service history.

First on my list is to solve the erratic idle and do the rear brakes. I'd greatly appreciate any links to threads that go over these procedures.

Here are some photos. I took a look at the idle air valve and was going to pull it out to make sure it worked, but, I came across something disconnected:





What piece am I missing here? How should this be connected?

 

That is part of the distributor venting system. It is connected via a plastic 90 degree elbow that is no longer available (I think). I went to my nearby parts store and purchased a brass 90 and a male threaded barb and made one that will never go bad. It connects to the AAV, then goes to one side of the distributor, then another nipple on the distributor has a vacuum line that goes to a small filter that looks something like a fuel filter you would see on a lawn mower. It won't cause your erratic idle. The AAV will however. Have you downloaded Kirby Palms book?

 

Congratulations on the XJS



Cheers
DD

 

That is sure a beauty. I'd class the fixes as fiddly and tough!!


1. erratic idle as fiddly.


2. Swapping out the rear calipers as tough. I got a rebuilt set with pads from Rock Auto. Main incentives, price and no core to mess with. I decided that doing the swap on my back was beyond my aged body's abilities. Armed out. $600.00 labor! OK job, but messed up the
hand brake. will I get under and fix it. Not yet....


Enjoy


Carl

 

Your car looks great. It will be well worth saving. I think that with the XJS we are reliving the experience of post WW2 car enthusiasts who found great barn find classics like V16 Cadillacs and V12 Lincolns that were virtually worthless at the time financially, but priceless for their heritage and beauty. Good luck. I've been going slow with my XJS as I've been getting some funds together.

 

Thanks Guys!

These cars are so undervalued at the moment IMO. The amount of quality and engineering one can get for the money at the moment won't last. I love the look too. FYI I've restored a couple of Porsches and this is my first Jag. One really nice thing is that this car wasn't built with little german elf hands ... I've got big hands and after doing some work on the AAV I'm really appreciating the space available to work.

So I pulled the AAV and it was stuck! I then WD40'd it, put a self tapping screw in one of the holes in the plunger(?) and got the thing to move nicely. I then boiled it and saw it close and open when cooled. Then I installed it back in ... and ... the RPMs still oscillate between 1000-1800 (roughly).

Anyone have next step ideas? I can hear the throttle position sensor "click" correctly - but, I haven't measured the resistance to make sure its not stuck at wide open throttle.

Regards,
Mike

 

I would dare say its still the AAV. But if you feel it truly is working as it should, I would start checking the throttle plate adjustments. I have always found that fiddling with these cars can go a long way.

 

Thanks for the book link - I'll be browsing it tonight. I can't say for certain that the AAV is 100% working. Is there a test I can verify the valve is working properly? Before I move onto the next investigation, I'd like to resolve the AAV as good (I don't mind replacing it, but I'd like to be sure it is faulty). It does move with temp, but maybe not enough...

Per adjusting the throttle plate - would the idea here be higher tension on the throttle cable such that we never rev too low?

Thanks,
Mike

 

Great choice of car. Providing you go through all that needs doing methodically and can do the work yourself, the parts are not idiotically expensive. The rear axle needs to come out to do the brakes, and while you are there do the lot: callipers, discs, radius arm bushes, change diff oil. If you search on here for XJS handbrake modification, there is a downloadable pdf that explains in detail how the HB works and how to greatly improve it if you are so inclined.


The Great Palm's book explains in detail how to set the throttle plates properly (basically use the throttle stop screws and a feeler gauge). Once the throttles plates are set, if the high idle remains, you have a stuck AAV, or the tickover screw on the AAV too far open, or a leak or all of the above.
The most probably cause of the vague steering is also dealt with in detail in the Palm book - being the rack bushes.
Depending upon your own requirements and inclinations, there is a great deal to be said for going through the whole car on the assumption that it has been poorly maintained, fixing all the known things that arise with the car under those circumstances, and after a bit of work you will have a reliable car. My list would include:
Fuel system complete clean
Injector flexible pipes changed, injector loom changed
On your car the Marelli dizzy cap and arm need careful inspection, changing if needed, and the amplifier looms also changing if they are cooked.
Thermostats change
100% coolant pipe change
Remove rad and clean out the fins and the crud in the oil rad and a/c condenser fins
Check front discs and calipers (also very carefully test the Antilock brake system which can go haywire, a search here will show how Orangeblossom rebuilt his actuator after a couple of scares)
Check balljoints and front suspension rubber bushes carefully
Clean up all engine bay earths very carefully, particularly the one from the engine via the subframe to the LHS lower chassis rail.
Test aircon carefully for full function, the system on your car is good, but various water valves and other bits can jam, vac pipes get leaky etc.


Seems a lot, but all doable with patience and dedication! And you will end up with a wonderful Grand Tourer.
Greg

 

The 'plunger' moves up-down to expose or cover a slot that admits extra air....which gives the high idle when cold.

As mentioned it could still be the AAV. Although you got the plunger (piston) fundamentally operational it may not be moving far enough in the bore to cover the air slot. When working properly only a very small portion of the air slot is left exposed when the engine is warmed up.

But, as Greg says, any air leak can give a high idle. If high enough....as in your case....the fuel shut off function of the ECU kicks in and the RPM drops. The fuel (injector pulse) is then restored, the RPM increases, and the cycle repeats and repeats.

Cheers
DD

 

Greg & Doug,

An air leak seems like a high probability root cause. I will see if the system will hold vacuum. Thankfully there is a nice sticker on the hood

Greg,

Thanks for the list! Sounds about right LOL. The person I bought the car from actually did quite a few of the jobs you mentioned (although one never knows the level of quality), he seemed like he knew enough to do some decent work on the easier stuff that didn't require the car up on jacks.

I'm going to drop the rear end tonight or tomorrow - and I haven't ordered any parts yet. Do you guys know of a parts list I should get on order? I've seen some rear brake 'kits' maybe this would be a good start assuming I don't find anything too nasty.

Mike

 

So I started inspecting some of the air hoses and found this:



I'm going to hack together a replacement (until I get good parts on order) and see what happens.

Mike

 

Hard to see exactly, but if the end of the rubber tube going under the throttle body is open, then that is your leak, as the spigot it should be attached to is open to air. The tube should be attached to aforesaid spigot that comes out of the bottom of the throttle body. Any suitable tube of the correct size will do if the tube is broken off, but the OEM tube is best as it has the correct 90 degree bend in it. Attach with a worm drive clip. The solenoid thingy on the airbox end opens up when the aircon compressor kicks in to ensure the car does not stall at idle if the compressor starts.


This is a useful site for parts diagrams: Find Jaguar Heritage Parts Online | Jaguar Heritage Parts UK


and this is the tube you need to connect up (diagram no 13):

Aircleaner-Rh-5.3 Litre - Parts For XJS from (V)139052 to (V)179736 | Jaguar Heritage Parts UK


Greg

 

Mike,
You will need discs and rebuilt calipers, Doug will know decent aftermarket places in the USA. Also small and large radius arm bushes, ONLY buy OEM metalastic items. All the aftermarket non-metalastic substitutes are total rubbish. Shocks and springs may be Ok, may not, take a look at them when off the car. Ditto the axle cage rubber mounts. There are 10 grease points on the rear axle, so give it a good greasing up while apart and check the fulcrums for play fore and aft. Everything is available quite easily.
Greg

 

What Colour is She?

Not the uber rare Morroco Red by any chance, it certainly looks like it from here.

If your getting a banging noise going over bumps, then it could well be the Shock Absorber Bushes on the Front.

Which could be completely worn away by now, probably one of the easiest jobs to do on an XJS and very easy to make your own by using a hole saw on a piece of rubber the right thickness.

That way you can 'Tweak' the ride exactly the way you want it by experimenting with different types of rubber, rather than just settle for OEM.

The piece of Rubber that I used was harder than OEM and now instead of wallowing all over the place She corners on rails.

 

Hi Orangeblossum,

This one is black with tan interior. I'll post some better photos when I get her out of the garage .

I think you're right about the front bushes - I'll have a good look up front in the coming week.

Mike

 

Hi All,

Made some progress yesterday. I replaced that broken hose with a better quality rubber generic hose and voila, erratic idle gone. No she warms up and sits at about 1100 rpms. Still seems too high but I'll have to do some research on this as well as further inspect the engine hoses. I did adjust the idle bolt in the AAV and did manage to reduce the idle just a little. I suspect the AAV, while now moving, is still needing attention (as superchargedtr6 menitoned earlier). So I'll have to figure out a rebuild or replacement...

Yesterday I managed to start on the rear brakes. Not as bad as I thought it was going to be, although I was hoping I wouldn't have to cut the exhaust. There doesn't appear to be a way to weave the rear exhaust outta there without cutting though...

Rear brakes are in *bad* shape LOL... have new ones on order.







Can't get that darned thing out LOL





Very poor condtion

 

each over-axle exhaust pipe needs to be separated from the box in the wing tunnel behind the axle, then it will come out. The pipe is attached to the top of the cage by a pin that just pokes into the fitting on the cage inside top. You have to pull the pipe towards the front to disengage the pin. Then the pipe can be wriggled out towards the front. All part of the XJS craft...
Parts 22 to 25 in this diagram. Parts 26 to 29 are fixed to the cage top.

Greg

 

Thanks Greg,
Per the exhaust, Unfortunately 8 will not separate from 7... I tried heat, force etc. Just won't budge. I tried to get it out all connected but no luck.

Btw, thanks for posting the diagrams, they're very helpful.

Mike

 

Just on the high idle problem, have you checked the idle switch is correctly set up?