1993 XJS 4.0. It's been over 2 years and close to $2500 in mechanics fees and I/they still have not found anyone who can fix my rough idle problem. I've tried several different shops and they are all willing to take my money but no one has found the problem. I will try again on this site.
It starts up immediately, but idles poorly, chugs for a minute or so, then the idle gets a little better, but still chugs at idle. Once I give it a small amount of gas, it smooths out and runs very good. It is very drivable in this condition, as I drive it several times a week in this condition, but it bothers me that at stops, it runs rough, till I accelerate.
Any thoughts on what might be causing a rough idle condition on my 93 xjs. I've replaced or cleaned just about everything, idle control valve, temp sending unit, computer, air intake, , throttle control valve, had all air hoses replaced. I'm guessing at this point, it's something small, air/fuel adjustment or maybe a relay. Any thoughts or does anyone know a very good jaguar car mechanic on the Southside of Chicago.

 

Did you replace the crank position sensor?
RagJag

 

Yes, I replaced the crank position sensor. I did replace it with a so called good used one. I might buy a new one and try again. Thanks for the reply and suggestion.

 

93greenconvertible, As I posted before on your problem, when I installed a new CPS the idle problem was instantly cured and has not returned for over a year now. The only reservation I have mentioned about this fixing your idle is that you have an earlier model as mine is a '96 and I don't know if the systems are identical.
Luck, RagJag

 

I just ordered a new CPS, so we will see if that is the solution. Thanks for the suggestion and I will post the results hopefully later this week. Thanks

 

My '95 4.0 runs great but often idles roughly. Tried several "fixes" but no big changes. Maybe I too should try a new Crank Position Sensor. Question: on e-bay they run (new) from $60 to $300. I try to save every dime I can, but want to avoid false economy, so which one? (I notice some have a business end that's right angle, others are straight.)
Thanks

 

I ordered mine from Rock Auto Online. The prices from Rock auto were also from around $60 to $150. They had pictures of each model and so you have to know which model your car uses. Besides the right angle difference, they also have some that use 1 screw to bolt it in or 2 screws, as well as the connections are also different. Some connections are flat 2 prong as mine was a triangle three prong. Rock auto has pictures of most of their products, so I just checked to make sure the picture was the some. It arrived today and appears to be the some as mine. I haven't had time to install it yet. When I do, I will let you know if there were any problems and if it corrected the problem.

 

I installed the crankshaft sensor this afternoon and did a hard reboot of the computer (removed the neg. side of the battery for about 5 minutes). As expected from the reboot, the car started hard, ran rough with idle searching, but after about 5 minutes, started to smooth out and run good, not great yet. It does seem to idle a little smoother, but I really have to drive it for a little while to let the computer to settle in. So far, so good. I just don't have the time today to take it out and drive it. I have my fingers crossed, that this might solve the rough idle issue.

 

We will keep our fingers crossed that you are at the end of a 2 year search for a smooth idle.
RagJag

 

I took the jag. out for a 10 mile drive to see if the computer could adjust the idle. It appears to be a little bit better, but still not perfect. I will keep driving it over the next week or so and see if it smooths out completely.
Unfortunately, my radio is now out and appears to not be getting any power. I posted my radio issue on another post, if anyone has any suggestions about the radio, please let me know.

 

Sorry about the radio not working. That may be a simple matter of a blown fuse. The idle problem on my '96 went away as soon as I cranked the engine after installing the new CPS.
I wish yours had.
Cheers, RagJag

 

Here's the update and all is not good. I installed the new CPS, it did not fix the problem. My radio quit working and now my engine is throwing a FF24 code and the car is going into limp mode. This has never happened before even when the idle was rough. I changed the CPS back to the first one and it still goes into limp mode. Did some research and hoping that it might be the ignition module. Ordered new/used module. Removed radio and checked all power, all was good, radio is trashed. Replaced with aftermarket radio, sounds great. Now if the car will just run correctly.
I own 2 Jaguars, this one and a 98 XK8. The XK8 has been in the shop for over a month, the mechanic can not find out the problem with why it will not stay running and this one will not run correctly at all. I'm very close to calling it quits with Jaguars, I love the looks and when they run, I love driving them, but this is getting very old with them breaking down all the time. Just venting!!!!!!!!, my frustration.
I think I'm going to take my Benz 500sl out for a drive.

 

93greenconvertible, so sorry the car will not run correctly. I know the frustration you are experiencing. These British queens seem to be quite troublesome. I also love the looks and driving experience but all the niggling things that stop working is a problem. My '96 has 92,000 miles on her which I can compare with my'96 Mercury Cougar with 149,000 miles. The Mercury has comparable equipment as the XJS, even independent rear suspension. All switches and buttons still work on this car and the AC is very cold even though it has not been worked on these 18 years. The heater and AC doors still work. I guess my biggest complaint about the XJS is the Delanair 3 system. I have not found anyone that have removed the system to repair it and replaced it.

The idle problem is being caused by something and this problem is fixable. I know because I finally got mine to idle at 600 rpm as it should. I wish we lived close for I would love to help you get to the bottom of this.
RagJag

 

Hello, I wanted to chime in on this.

Our '95 4.0 also tends to idle roughly once it has been running for awhile.

It starts up strong and will sit at a fairly low, even idle with no issues.

However, once it has been running / driving for 20-30 mins, the idle starts to really get cranky and it will tend to stumble or stall at stops signs. This is very frustrating indeed.

Does that sound like your problem, 93Green? I know some of the systems between our two cars might be different, but let me know about how and when you have the idle problems and what you have tried or plan to try. I am considering just replacing the CPS on ours per the suggestions of others to see if that will do it. Thanks.

 

93green, it is really a question of degree, but there was a repair Jaguar published back in the day for an idle quality complaint. It involved changing the cam timing slightly. They made the same change in production, and it effectively 'detuned' the engine a slight bit. But the idle complaints stopped.

Some people elected to make the change for a smoother idle and slight power hit, some decided to live with the idle quiver.

Here is the bulletin describing the repair. As I said, it's a question of degree. Is it really too rough, as in something else wrong, or could this be your condition??

Cheers,

 

There was also a condition that could crop up when the engines were hot, especially when coasting down an off-ramp. The EGR valve would hang open or slightly open and produce a pretty good rough idle, some would even stall. Carbon build-up on the valve pintle was the cause. Sometimes it could be cleaned with a carb cleaner, sometimes it took another valve.

 

XJRguy -

With regards to that bulletin, does that apply to 95 4.0's or up to 93 only?

Also, in the part where you mention the EGR valve bing clogged, what is the best way to check it or clean it?

Thanks.

 

This applies to the AJ16 engine that has the gray cam cover, not the earlier AJ6, which has a black cam cover. The AJ16 came to the States in 1995, a bit earlier in Europe.

The EGR valve is circled in the attached picture, the other pic shows the engine number. If the valve is removed and upended, you can gently push the pintle up into the valve. It should easily follow the probe you use to push it. If it sticks anywhere, it's a problem. Sometimes it sticks so badly you have to tap the valve to get it to close again.

Cheers,

 

93greenconvertible,

Sorry to hear you've got problems. Just a thought:

I know you've got an AJ6, but there are lots of similarities to an AJ16 of which I know a bit more about.

There are a number of components thst influence the idle on an AJ16. Some of these are "fixed" and shouldn't vary by temperature, some are directly linked to temperature and then there are some which shouldn't change by temperature but might inadvertently because of thermal expansion.

The ones that really shouldn't change are the crank position sensor and the ecu.
The ones that do get influenced by temperature are the engine coolant temperature sensor and the idle air temperature sensor
The ones that Shouldn't but Might are the the throttle body, the throttle body position sensor, the idle air control valve, the mass airflow sensor and the egr valve.

So there are 2 temperature related sensors that could be playing up, a few valves and throttle body components that could need cleaning and some electrical connections that might vary if they get hot. In addition,you may have an air/vacuum leak that opens when hot, or wiring such as a coil or plug lead which breaks down a little when hot.

You could work through these systematically or maybe just get a specialist to hook the car up to an Autologic or similar to monitor the readings on the various components when hot. That might be the quickest and easiest way to crack it.

Good luck with sorting it.

Paul

 

Everyone thanks for all the good information. I'm waiting on a ignition control module that I ordered and will try that at least to get the XJS running without going into limp mode. Unfortunately, I've posted this problem about a year ago and every part this post has been mentioned, has been replaced(at least once). As far as specialists to find, I've lost all faith in so called specialists, unless someone wants to NOT charge me unless they fix the problem. I've spent thousands already on so called specialists and not one has fixed the problems, but all have charged me, stating "that's the best we can do". As I mentioned before, 2 jaguars and both have been looked at by specialists and both still do not run or do not run correctly. After installing the ignition module, if that does not correct the problem, I'm going to start from the beginning again and start testing all the components again myself. Maybe I will luck out and find something. Thanks again.