1986 Rough idle, and will only rev in park and neutral

iI suppose I have a lot to learn and a lot of work to do on my new 1986 jaguar xj-s, but I suppose I’ll start off with how I got it. An older man used to be a fire fighter got it from someone they know and drove it for a year or two before it sat in his driveway for over a decade. Whereas now I have the car in my hands the car has almost 32,000 miles on it and has been left outside, so there has been weathering to it. But besides that I brought it home and put a new battery in it, and it fired right up for me with the exception of a lot of ticking, which I found out a mouse had chewed up three spark, plug wires. I’ve done an oil change and I replaced those along with the coolant temp sensor. (CTS) which seems to have done nothing. I need it unplugged for the car to even start let alone run well if it does start with it plugged in it will idle hunt at about 600 to 300 RPM but as I take it out and idles between 700 and 900 , nonetheless, I put it in drive and take it for a spin just up the road, and the car will not let me go above, half throttle, nor let me hit it harder than a light acceleration , until just recently I thought my fuel pump failed on me because of the loud screeching noise it was making as I took it to the car wash, and when I turned it back on the car would start right up but idle hunt and now I have zero acceleration and in drive the car will only creep forwards, but in neutral and park, I have now replaced the fuel pump, but it will rev as long as I barely touch the gas on and off until about 2000 RPMs it will then let me lightly touch the gas to rev the motor, but any kind of hard acceleration on the motor it will’s daughter and act like it’s gonna die. If held down long enough and almost sounds like there’s some kind of leak. Starting the car and putting both hands behind the exhaust I have found my passenger side seems to be blowing out cold air. I have just found this out the other day.

any help would be greatly appreciated. I have been stumped and reading post after post to sadly no avail

Coil and spark plugs? What condition is the distributor cap and rotor? Is centrifugal advance not working? They can seize in these cars.

I am assuming you have Lucas ignition V12. What year is your XJS? Makes a world of difference for us to help.

it’s a 1986 xjs
i’ve checked a spark plug on both sides of the motor. they look like they’ve been replaced before they’re NGK brand spark plugs and they’re both a light brown color i haven’t got into the distributor yet but i will take it apart and give it a look when i get home, also what and where is the centrifugal advance located

here’s a picture of the passenger side spark plug the driver side looks just the same

Not too bad, but they look old. Gap is very important for these engines. That gap looks too big? Supposed to be .024"

Download Kirby’s book, lot of good info. It explains the distributor in detail.

okay i’ll have to download the book, and do a bit of reading on it. thank you!

In a nutshell, the grease Jaguar used, due to heat, will eventually seize centrifugal advance. You’ll need to disassemble, clean, and oil with synthetic oil to prevent.

The “could be” list might get long; and you may have a stack-up of different problems.

Personally I would begin by removing the fuel filter and emptying the contents inro a clear container. What you see or don’t see will dictate your next steps


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My 88 XJS sat for seven years, and was very neglected. I faced similar issues.

Took me 6 months to get running ok to drive again. Now 5.5 years into it, I’ve replaced quite a lot. These cars are at the age of an almost total restore. So be ready.

i forgot to mention i’ve replaced the filter and took the slump tank out and cleaned it. i tried with the gas tank itself but it wouldn’t budge out of its prison cell in the truck, also as much as i wanna drive it today i know it’s gunna be a while so if you have any thoughts on anything i should replace i’ll gladly look into it and figure things out

also is the centrifugal advance inside the distributor? that may be a dumb question but i’m young, dumb, and wanting a challenge to work on

Yes. Centrifugal advance is an old fashioned way to advance the timing at higher rpm.


awesome thank you for the info!!! i’ll be home in a couple hours i’ll report back with what i see when i take my distributor cap off and clean up the centrifugal advance

Caleb, just FYI…passenger side would be on the left in UK. On the right in North American market.
If you learn to use A bank and B bank it doesn’t matter which side the steering wheel sits.

There are many variables involved when talking about an XJS. Different v12 engines, different inline 6 engines, Coupes/convertibles/targa, and more. Better specificity from you yields better answers from the forum.

Keep asking…these guys are awesome. Also utilize the “search the archives” feature…most questions already answered to some extent therein

i’m in north American in the united states😁 i am unsure which bank is which entirely i haven’t done but about a months worth of research myself when i bought the car in january but it would be the right hand side of the motor if we’re in the driver seat

also i’ve taken apart the distributor now and my cap and button don’t look that far from being bad i’ll send a couple pics of them but my issue now is how do i take the button off to clean the centrifugal advance, my button moves a slight bit up and down but won’t come off i’ve took of the plastic protector under it to get to the bolts inside but not sure if that’s the way to take it off

as i was taking it off the gasket broke to it do i need a new one?

Ooo, you may have an original bakelite cap. Keep it, they don’t make 'em like that anymore. New ones crack within a few years.

Gasket usually breaks. Yeah, good to replace. There is a slight draw of air on the distributor to keep it cool inside. The fresh air is hooked up to a tiny filter. Without the gasket, your distributor may suck in dirty air within the vicinity.

okay great, i’ll replace it. but how do i get the button off so i can clean the inner parts of it or do i not need to from what i see everything looks very clean and nice under that cap other than the obvious wear

Before pulling the distributor, i would read and re-read Kirby’s book about the distributor. That’s what i did. Lot of specific things inside that distributor to learn.

Pulling the rotor needs to be done just right. Takes a lot of pull, but you can’t just pull or you can stretch the centrifugal springs. You need to pull rotor while pushing down on what it connects to, if that makes sense.

Will be much easier servicing the distributor on the bench (once you pull rotor and remove shield, you can)

okay do i just need to pay for the subscription on the adobe acrobat?