I have been using my 1998 XJR regularly, in fact any excuse to go somewhere in it... even did a 2000 mile trip towing a 25 foot caravan round Ireland last summer without issue. I have a problem though... for the last 2 years from October through to April the guages stop working, it wont come out of park, it sometimes changes gear with a bang, the message panel is scrambled, it wont go over 60mph, all the dash lights are on, the heater wont work, suspension very hard at slow speeds.... Then after a certain number of miles, more in cold weather, less in warm it all comes ok again. If we have a particularly nice day, it will be fine from the start, it might even come out of park without being poked with the spare key!
Any ideas?

 

It sounds like you've got a number of separate issues.
Firstly how old is the battery, these cars are sensitive to voltage drop and will display all sorts of issues if the battery isn't in top condition - a minimum 12.5V so if it's old or suspect, change it and see where you are with the faults. (scrambled msg centre for example)

Not coming out of park, can be a sticking interlock solenoid, do a search on this part within this forum and how to access it to test/replace.

Changing gear with a bang - somewhat more serious, the ZF transmission fitted to your car has a very well known fault in the control valve body, the solenoid wears a ridge in the bore, sticks leading to a pressure spike which gives hard shifts, and leads to a broken circlip which leads the A drum to spin free and damage it's outer edge. At this point it's a gearbox rebuild - But - there is a kit offered that can address this offered by TransGo, again searching the forum will get you up to speed on the fitting.

Heater - a couple of parts to check, the auxillary pump which sits under the expansion tank, could need new brushes, or a simple clonk with a hammer shaft while energized to get it to run, also the heater control valve - both of these things to check working.

Hard suspension - I assume you XJR is equipped with CATS suspension (wires going to the tops on the front shocks) - it's default setting is Hard, so see if you've got wires plugged in, more info needed on this issue, maybe specialist diagnostics to identify the fault.

Another thing you can try is spray contact cleaner on all the connections you can access under the bonnet, as it sounds like oxidization is causing a few issues here.

Hope this helps

 

Thanks for that but, As soon as the guages come back on and all the dash lights go off everything else comes back on.. heater comes on warm, gears work seamlessly, suspension correct, all the dash lights go out and the message screen will work the next time you start it up. Its seems everything is in limp mode til the speedo fires up. It will not come out of park while it is in this state. Nice day yesterday and it only took a few minutes for it to sort itself. whereas two weeks ago on a cold day it took 50 miles.

 

So temperature/instrument pack (IPK) fault from the added info?

I've mentioned the fitness of a battery - what's your info on that?

The IPK is a major CANBUS item, has there been any work in the dash/centre console? A quick re-seat of it's connections at the base with contact cleaner might sort it, or a new IPK from a year related XJR.
To change out the IPK you'll need the same program code listed in your car's boot - there is a white sticker around the spare wheel well, look for IPK---/--- (First set of numbers part number, second set program code) it needs to be exact for it to work.

I would suggest contacting EuroJag for a replacement, as they carry S/H IPK's and can usually match the one from your car including mileage (roughly)

 

Took the car to local motor factors today to have an in car battery check. Good quality battery from them was fitted a year ago as the previous one kept going flat. All functions came on 5 minutes after leaving home and was behaving fine at its battery appointment. The check revealed that the 850A battery was at 12.58v and 710A and the machine said the battery was good and needed a recharge!?? Other checks revealed that the battery is at 14.13v when running and 14.06 with the headlights on.. battery went down to 11.22v during cranking for 1.06 seconds. I wonder what the battery check would reveal while it is misbehaving? Never been in about the dash area in my ownership. I like the sound of the IPK connector because earlier this year during our Mothers Day trip out I got frustrated at the lack of heating after 70 miles and gave the top of the padded dash a good thump and all the guages fired up, all the warning lights went out, we had smoother suspension and normal gearchanging and more importantly warm air out of the heater. Incidentally, the fuel guage is never affected.

 

The wood trim surrounding the gauges is held with clips, if you lower and extend the steering wheel column you have access. Gripping the wood panel between the gauges and a good sharp tug should get it free. From there you'll see 2 plugs at the base of the IPK, carefully ease them off and spray contact cleaner/reseat and see how that goes.

 

Thanks Sean... going to try that over the weekend.. and give it a test run on Monday for a May Day day out with the family.