I'm just checking in. I'm about to change my sensor and the engine is cool, it's been about 4-5 hours since I have driven it. Being about everything I do on this car is new to me, I would rather ask first to see if there are any surprises. Being this sensor is fairly high above most of the cooling system and I took the cap off the intake for coolant I figure there should be no pressure, but I'm wondering if it is still going to make a big mess? Battery is disconnected so hopefully it's a simple swap? Anything else I need to be aware of?

 

Put the cap back on tight before you change the sensor Then, when you remove the sensor, air won't rush in and allow coolant to drain. Very little coolant will escape as a result. Just have the new sensor in your hand and swap them out quickly.

 

It's done. On my first post I had said that the car was stumbling a little at idle and it was suggested that I replace this sensor. I replaced the sensor on the top of the thermostat housing with the two wire connector. The car did seem to drop about 200 rpms, but that slight stumbling is still there. Although I didn't really give it time to warm up adequately. I checked the sensor and it is deep enough into the coolant. There may be more than one sensor that needs replacing. I'd rather put new ones in it being I don't know how long it's been since the last owner did it. Maybe I need to take her out and drive her a while to give it a chance to cooperate.

 

Sounds like you have t given it a chance yet.

Next sensor on your list would be the IACV, Idle Air Control Valve. Be careful with that one…the 5.5mm bolts are loctited in from the factory, so they are likely to break. Heat them up nice and hot before you try to remove them. If you’re lucky, you won’t need to order timeserts or helicoils to repair the threads!

Slight stumble could also be the coils. Have you checked them for oil? The gaskets at each of the plug cylinders leak oil when they need to be replaced. That drowns the coil in oil making it harder for them to do their job.

or one of the coils is beginning to die. You can test this by buying a new coil and replacing one at a time, see if the stumble goes away.

It could also be the oxygen sensors? When was the last time those were replaced? They are not made to last forever. 60k miles is what they should offer you, but they tend to last longer than that….but not forever.

 

It seems like a lot of people have a problem with the bolts snapping off, and that can be a nightmare. I have read a lot about this sensor, but nobody says where it is located.

 

Hi 93xjs6cyl

Here is a pic of the location of the Idle Air Control Valve on an XJS V12

So yours should be in a similar location

As for undoing the Bolts to take it off 'Rather You Than Me' as there is too much risk of Snapping the Bolts off, so I would leave it well alone if I were you

What Engine have you got AJ6 or AJ16

 

Have a look at the following, including idle adjustment.

But remember, idle speed problems are usually caused by air leaks, coils, plugs, sensors etc.

So get everything checked and operating perfectly first before you start messing with ecu settings which are not the typical cause.

Cheers,

Paul

 

You should get yourself a Service Manual. The one with the green cover. It's available on eBay. It will likely set you back less than $100, but it has a lot of useful information.

If you're looking for the part, you can use google for a picture of the part and then do the Where's Waldo in the engine bay. You have a six cylinder, so it's not quite as difficult as the v12.

 

I have that manual, it really doesn't give much information. Most of the time I have to figure out my problem myself with the help of this forum. It's about the same as Hayne's manual. I have the 4.0 engine, so I think that is the AJ16 engine. I'm going to try checking some other places before I even consider messing with the Air Control Valve, it's too risky. The biggest difference I have achieved so far with changing sensors is a difference in RPM's. My car doesn't have individual coils, it only has one and my car runs too good for it to be giving me a problem. Today, I plan on taking the valve cover off and see if it is leaking oil into my part plugs again. I cleaned that up once and at the time I found my cover was loose so I tightened it down. My car runs great even when I use "Sport", the only problem I have is the slight stumble at idle. It doesn't stall at stop lights or hesitate at all. I don't think I will use "Sport" any more, that just seems hard on the car and it runs fast enough for getting around. I need to get another set of the round seals that go around the spark plug holes. That might be my problem. I remember cleaning it up made a difference before, but I'm not sure if it took the stumbling completely out. If it is leaking oil into my spark plug holes again, I will clean it out and see if the stumbling goes away. If it's not leaking, then I need to keep looking for the problem.

 

The green book is 90% AJ6 (your engine). The last 40 pages are AJ16 updates.

That book is pretty darned good. I’ve never seen the Haynes manual, but I can’t imagine it would be close.

The Sport setting just changes the shift points on the transmission. That’s it. Doesn’t do anything else.

Checking for oil filled spark plug wells is a good idea. You may as well get a new set of those gaskets. That could very well be the cause.

Good luck and keep us posted on your progress!

 

I didn't mean to step on anyones toes. I'm used to buying the original shop manual when possible. I've worked on a lot of American cars as a hobby and this jaguar is different. Maintenance and working on them seems easier. Understand them is different. I would imagine that this manual would be easier for me to work with if I was used to working on British cars. I still have an MG out back that needs my attention, but if you look under the hood and you look under this hood, you might not even think you need a manual for it. As far as "Sport", I'm sure it will come in handy when I need to pass someone, but I'm not going to whip a horse every time I get on her back. I hope this car last a long time. Well, I better go check those plugs.

 

Well, I just finished round two with the valve cover. I had just a little oil sneaking by on the first cylinder closest to the window, all the others were dry. Also, I doubt seriously that there was enough oil to getting into the cylinder. I cleaned up what there was with a paper towel and a small screw driver and it was very little. I made some 1/8" thick round rubber gaskets to go between the seals and the valve cover. The rubber is of good quality, so I figure the worst that could happen is it I might get a little oil to sneak by them. I'll be taking the car out tomorrow, so I will look and see if I see any oil is starting to go towards the plugs after my drive. The new gaskets aren't going anywhere, they have the plug wires keeping them in place. So, anyway I started up the car and It started on the first try like it has since I first cleaned up the spark plug wells. It seemed (I'm not going to hold my breath) like the stumbling is still there but only happens about once every 10 seconds or so now and it's not as pronounced. A few days ago I took out all the relays and cleaned up all the contacts which was quite a job. A few of them were pretty dirty. The one that seemed to make the most difference was to my air conditioner. It used to be real wimpy, but now it will almost blow you out of the car. That's a good thing being it gets up to 110 degrees here in the summer. I like those relays, they are built like a tank. The more I work on this car the more I like it. It has about a 1,000 relays and sensors, but usually all you need to do is replace the relay or sensor and you are good to go. Pretty much plug and play. Oh! I also, changed the oil and filter the other day, I would think that should make it easier for the oil to sneak around.

 

I used to have an idle stumble every 32 seconds. It was worse when the radio, AC, headlights, etc were on…occasionally enough to stall the car out at a red light!

It was a problem 2 shops, my local and a Jag Specialist could not solve! A third shop, also a Jag Specialist was able to pinpoint a failing intake manifold gasket.

 

Good to know, thank you very much.

 

Wow! That must have been a real pain. I'm hoping my problem is being resolved little by little. In the last month I have done a lot to this car. Usually, the biggest change that I have noticed has been a change in RPM,s and the fact that now it always starts on the first try. I don't even have to wait for the fuel pump to run a little before I turn over the key. I just turn the key and it starts right up now. Right now it's idling right about 800 RPM's and I'm good with that. I need to take it out and just drive it for a while. My next two items on the list are the fuel filter and a new set of oxygen sensors. Either one could be administering this hiccup. I have to remember that some of you guys have a European car and mine is American. Also, my car vin number is right at the changing point. That's why I didn't find my fuel filter in my right front wheel well. Although I did find a large round canister, but it had electrical wiring hooked up to it. I need to figure out what that was. I still need to jack up the car so I can change my fuel filter. I also need to check the compression on my cylinders. That always makes me a little nervous. My car is just now coming up on about 99,000 miles and honestly, I don't know if that's 99,000 miles, 199,000 miles or 299,000 miles. So, if my compression is good or not, that should tell me.

 

Had similar issue with my 92/93 4.0 convertible earlier this year. Idle speed valve change made major improvement, but found serious leak from the bottom lip of the black bellows where it connects to the intake, There is a specific procedure for changing out and resetting the idle speed valve, but not difficult. There is an allen screw hidden in the top that makes idle level adjustments. If you're in Maricopa county, there are a few shops (particularly East Valley) recommedable.
Dave in AZ

 

Sounds like quite a few guys have had a problem with taking this off. Snapping the bolt off in the housing would be a nightmare. The stumbling has seemed to want to continue no matter what I did, so I figured I had to take a chance with the (this thing seems to have a few names) idle speed control actuator. First I took a punch and tapped all four bolts a few time in moderation, Then tried to turn them, slowly they all started to turn so I soon had it off. Then when I could see the connector latch, I disconnected it. The gasket was stuck and smashed, so I slowly worked it off. I got some gasket material and made a gasket (easy enough). So now I had this thing in my hand I took it to my bench to check it out. Now I was going to try to take the step motor off. I had a much harder time taking the bolts off this one. I tapped the bolts several times with a hammer and off it came. I sure could understand why this thing was throwing a fit, it was filthy. Mine is all metal except for the connector, so I cleaned it out. I put it back on the car and started it up. The car was running about the same as before, but now I notice a slight hissing sound from it that I didn't remember hearing before. It is supposed to let air pass by, so now I guess now it is. I had counted the turns on the adjustment and marked it when I took it out to clean and I put it back at the same place. I let the car warm up for a while then turn the adjustment in a little at a time, I could tell it was closing off the passage, the rpm's dropped and it didn't seem to like it. So, I started to open it up a little at a time. I can hear the slight hiss, the rpm's went back up and the stumbling seems to be all but gone. It is now open about 1/10th of a turn more than when I took it off. The real test will be when I take it out for a test drive tomorrow. It will either run about the same, run better, or stall. I'm taking my Allen wrench with me. So, my question is... being it's adjust the air mixture, do I keep an eye on the spark plugs to see if I have leaned it out?

 

I don't think you'll now see a leaning of the mixture through the plugs in normal running. IME the 4 litres tend to run slightly rich at idle and then tend to lean out at very high revs. As mentioned, these engines are not really designed to have "manual" adjustment of the mixture. The ecu controls the injector pulse width based on the input from the various sensors, coolant, MAF etc. Most idle stumbling is usually the result of loose vacuum, excess air or manifold leaks etc. Hopefully what you've done has cured the issue.

Cheers

Paul