January 21, 2014. Bought my Jaguar X300 Sovereign 4.0 in 2009 and have had 4 years trouble free, and 1 year troublesome motoring. The current state of play is that it idles too fast, about 1'500 rpm at start, about 3'000 rpm after driving if car is not in gear. It is also running rather roughly. None of this seems to be affected by whether the car is cold or warmed up. Also transmission warning light flashes constantly although transmission is not in safety mode, and gears change OK. This all started a year ago, and in that time the following parts have been changed:

1) All 6 coils (new generic part)
2) All 6 spark plugs
3) Throttle position sensor (ref. JLM12074 – generic? original? new I think)
4) Mass airflow sensor (ref. LHE1620AA – new generic part)
5) Idle speed control valve (ref. JLM12185 - new original Jaguar part)
6) Rotary transmission switch (ref. LHE6201AA – new original Lucas part)

At first the coils and spark plugs seemed to cure what seemed to be just a misfire. But the problems kept coming back and only got worse. During the summer the misfire got worse and worse, the transmission became tempermental, flipping in and out of safety mode, the instruments developed christmas tree syndrome, with all warning lights flashing on and off, so I decided to have it looked at by a garage. I recovered the car from a garage early December, where it had spent 6 weeks, and where it received parts 3 to 6 listed above. The car is in its current condition since I picked it up from the garage (for obvious reasons, I don't see much point in giving the car back to them).

I'm beginning to wonder if the engine ECU should be changed. Does anyone have some advice they can offer? Can I just switch a new one for the old one, or will a new unit need programming?

Any help you can offer is obviously appreciated.

 

Much has been written on here about coils. There are varying opinions, but the general consensus seems to be that if you use wrong ones, ie; brand, oem, spurious etc. it can cause symptoms such as you are having. Also the "Christmas Tree" syndrome seems to be connected with bad coils also. Similar problems have also been reported after changing spark plugs. Some X300's seem to dislike certain brands!

So, that's where I'd start looking. Another thing is,have you had the throttle body cleaned?

 

In my experience, most "hard to find" problems are really two co-incidental problems making troubleshooting very difficult. You did not say if the Christmas tree still exists, but if so, I would say you might well have a bad replacement coil.
As to the high idle, if you did not do a TPS calibration procedure with the dealer software, it might very well be thqat the new TPS is miscalibrated.

 

I would suspect the following:

The current state of play is that it idles too fast, about 1'500 rpm at start, about 3'000 rpm after driving if car is not in gear.
Check the following:
- Bad Fuel Pressure Regulator
- Bad Temperature Sensor
- Slow reading O2 Sensors

It is also running rather roughly. None of this seems to be affected by whether the car is cold or warmed up.
Check the following:
- Check Air Intake boot/hose to throttle body for vacuum leaks by spraying brake fluid around clamps and boot.
- Consider installing Champion RC12YCC spark plugs
- Check Temperature Sensor is working properly
- Check fuel pump relays are not sticking and changed them from the blue DAC 7686 to the new sealed ones.
- Slow reading O2 Sensors

Also transmission warning light flashes constantly although transmission is not in safety mode, and gears change OK.
Check the following:
- Check to see if you have the blue DAC 7686 relays for the transmission and consider switching them to the new black sealed ones.

This is all that comes to mind when I read your post.

 

Thanks to Sogood, Sparkenzap and Dpena for your replies.

In no particular order:

Aftermarket coils - yes, I have my doubts about these, and am seriously considering replacing with original Lucas parts. However, they are not cheap, and whilst quite possibly implicated in the engine running roughly, they presumably are not causing the too fast idle. Also, the instruments are behaving now execept for the transmission warning light, which may well not be a problem with the instrument panel. If I can sort out my idle issues, then I think it will be worth changing.

Spark plugs - I had a garage change these as I was scared that dirt would fall in the engine if I did it. As a result, I don't know what brand was fitted, but maybe I can find out.

More than one problem at the same time? Given where I find myself now, I would not be at all surprised. It certainly does not make things easy.

Sparkenzap and Dpena then mention a good few points which, at my level of competence, sound like reasonable suggestions but are currently beyond my capabilities. I will either have to enlarge my capabilities or find a garage to check those things.

Thanks again guys. I hope to report back with positive news sometime soon.

 

and no one thinks it's my ECU then?

 

Well, we *have* heard reports of corrosion on the ECU connector pins. It would be worth investigating.

Cheers
DD

 

Also, for the high idle, slacken and then readjust the throttle cable (or throttle cables if you have traction control)

I've had high idle problems a couple of times. One time, almost on whimsy it seems (this was years ago so my memory is foggy) I readjusted the cable and that fixed the high idle. I can't explain how or why the fault occured.

At minimum you could disconnect the cable from the throttle body, start the engine, and see what happens.

Cheers
DD

 

Jeff,

Sorry for your woes. If I understand the timing of events, you first had what you thought was a misfire and had the coils and plugs replaced?

Then after a while, the misfire returned and got worse and you got the Christmas tree lights syndrome? To me this is one of the hallmarks of coil failure. However, you did not state whether the coils had been changed again? Instead the garage changed the TPS, MAFS, ISCV and rotary switch? This is a bit baffling but would go a long way to explaining the high idle condition which I gather was not present previously? Unfortunately when a garage just throws parts at a problem they often mask the real problem or create new ones!

I think you are correct in thinking that after addressing the high idle, you may have to change a coil(s) again.

As Ross stated, quite often after after changing TPS, a recalibration is necessary and can only be done with dealer level equipment. You can however, measure the output voltage of the TPS and this will give you some more clues.

Also the ISCV may have been improperly installed or may be defective in some way, again dealer level equipment can check this.

Another common cause of high idle is an air leak somewhere after the MAFS, often one of the vacuum ports or the intake manifold gaskets. Easy to check by spraying some carb cleaner around the area.

Do you have a scan tool? If not, get one and look to see if there are any codes displayed. Often on the X300 there will be codes recorded but the MIL light is not illuminated. Also a scan tool will be able to give you some real time data from many of the engine management components.

The main thing here is to gather more data before throwing more parts at it. I would not change the ECM at the moment as you may mask the problem or make it worse.

Also the transmission light flickering may be related to the replaced rotary switch. There is a special alignment tool needed to properly set the switch, it's possible that it was not set correctly.

 

96 vdp USA 4.0

I would like to know where I can get these new relays?

Fuel pump and transmission

 

I don't really have any new suggestions, other than that you could have a look for arcing at the coils - which would be a certain sign of failure there.

& I wouldn't be spraying brake fluid anywhere!

 

+1 on that. Not good for sparks and paint !

 

Sorry,,, I stand corrected and should not spray brake fluid but carb cleaner but insure real hot engine areas are avoided to avoid a potential carb cleaner ignition.

My intent was to primarily spray the carb cleaner around the intake boot to insure there are no vacuum leaks. You would know there was one if the engine idle rises suddenly then drops back down.

My apologies once again.

 

Refer to this Tech Bulletin:
http://www.jagrepair.com/images/TSB/...ue%20Relay.pdf

This should explain everything about the "Hella DAC 7686 (blue)" versus the "sealed Hella (black) LHF 6703AA" relays.

 

You can locate many more helpful Jaguar X300 Technical Service Bulletin (TSB) at the link below:


Body, Engine, Drive Train, Interior Repairs
JagRepair.com - Jaguar Repair Information Resource

Electrical, OBD Codes, Tech Guide & Spec Book
JagRepair.com - Jaguar Repair Information Resource
Technical Service Bulletins (TSB
JagRepair.com - Jaguar Repair Information Resource

 

Thought I would update you.

After scratching my head a lot and swapping coils around, etc, etc; I etook the car to a local independent Jaguar specialist who, in hindsight, I should have gone to first. After discussing the story up to that point, he spent a good few hours looking at the car and not finding the problem. Then he borrowed the ECU out of another 4.0 naturally aspirated X300, tried it in mine and found that it solved the problem. I have subsequently sourced a used ECU from another Sovereign and the car is now pretty good, running on its original coils which the garage guy preferred to the after market replacements I had put in. I wondered about that, so I tried the after market coils and they were not good at all; lumpy running, stalling and christmas tree lights from those, so now back on the original coils with irregular odd misfire which is only at the level of an irritation. I would like the car to run better than that, so I'm trying to work out how to source coils which will correct the problem and not fail in a short period of time. I have seen a lot of discussion about coils elsewhere in these forums, so they are obviously problematic. It seems that it is so difficult to source good ones, I am wondering about obtaining some used ones with the expectation that some will be good and some not. The ECU, by the way, was a straight switch of pieces; no programming or anything like that: old one out, new one in, finished. There was no corrosion on the pins or anything like that; it just didn't work any more.

I still have the flashing transmission warning light and intend having the relays changed, assuming they are the old ones, as mentioned by Dpena.

Thanks to those who responded to my post at the beginning of this year.

 

Replaced the coils with Lucas branded (but clearly not the same manufacturer as the original) coils from British Car Parts a couple of weeks ago. Car is running very nicely up to now....

 

Glad to hear you've been successful in sorting out your problem. And now you have the added benefit of having learned another few things about your car!

Happy motoring!

 

Yup, certainly learnt a thing or two along the way:-) I'll update if the coils don't last. After all I've read, I'm somewhat paranoid about them.

 

Hi, I bought a sealed black relay to replace the old blue one. I now have a Jaguar maintenance manual, but have not been able to find out exactly where this relay lives so that I can change it. I guess they assume a certain level of knowledge which I do not possess:-) Can anyone direct me to the correct location?