Thanks for the update.

Sorry to hear work done to date hasn't resolved your issues, but wait to hear how it goes from here.

Best

Jim

 

I am still waiting for the new O2 sensors to be delivered, but at the suggestion of my son-in-law, Chris-the-Volvo-Tech, I disconnected the two upstream/front sensors to force the ECM into using a default fuel map. Well, the XJS started right up and idled smoothly with the sensors disconnected. I reconnected the sensors while the engine was running and within 20 seconds the loping idle had returned. This is good news and quite damning evidence that the O2s are causing the ECM to hunt for a fuel map based on the flaky signals being sent by the current O2s. I hope to have the sensors replaced this weekend. I will update.

 

here's hoping........

 

I installed the front two O2 sensors. With great anticipation, I started the XJS. It started right up and idled fine until the ECM started trying to lower the idle to the normal level. With great disappointment, the loping returned, but it is not as pronounced as it was. So, I let it sit and idle for about 15 minutes or so. The loping began to minimize and after dying a couple of times while idling, the idle seemed to be stabilizing a bit. It seemed that the ECM wasn't hunting as much. Sooooooooooooooo, I took it for a drive. It drove well and did not die at any stops. It did stumble a tiny bit at a couple of stops when returning to idle speed. After I returned, the idle was a bit more stable, but not as smooth as it should be. There seems to be a random miss/partial misfire that happens while idling. This misfire does not seem to be tied to any particular cylinder. I disconnected each plug coil in turn to see if it worsened the idle. They all did affect the idle so they all must be firing.
So, at this point, the only things that have not been replaced are the downstream O2s (I will get to them later and disconnecting them had no impact on the idle whatsoever. They are a BEAR to get to), the MAF and the ECM. I do plan to go ahead and replace the back two O2s because they look so old and I plan to drive the XJS more to give the ECM more learn time. Since I don't have access to a Jaguar PDU, maybe the ECM needs more time to adjust to its new running environment. Maybe the XJS needs an Italian Tuneup.
I wish I had great news, but I don't. No silver bullet.

 

Sorry to hear that, although they did help some as you say and probably long overdue for replacement by the sounds of it.

I keep reading your posts with interest and admire your determination to chase this down.

Hope to hear...

 

It's the downstream O2 sensors that do all the work.

The upstream sensors are just there to make sure the downstream sensors have not failed. As long as the downstream numbers (after the cat) are different than the upstream numbers (before cat) the computer will believe things are ok.

If there was a pair of sensors to replace first, it would be the downstream sensors.

Thanks for the continuous updates... It will undoubtedly be a huge help to others in the future.

 

UPDATE: I installed the two downstream O2 sensors yesterday afternoon. I started the car, it ran smoothly for the first 30 seconds or so, then the ECM began trying to bring the idle down to specs. It began to lope heavily.
But all is not bad, I hope. After it sat there and idled about 15 minutes, I noticed the following:
1. The loping began to diminish
2. Every 32 seconds, the rpms would drop momentarily by about 150 rpm, then return to 700 rpm with a lope. The lope would then begin to diminish and the cycle would repeat every 32 seconds (Lather, rinse, repeat). I am speculating, but the 32 seconds might be the cycle time that the ECM tries different fuel mappings. If it does not like the results, it changes to another, and so on.
3. Once the idle loping had diminished enough, I was able to detect an intermittent ignition miss. Definitely a negative contributing factor to the problem symptom. I thought I had heard this miss before in the process, but had not been able to isolate it. This time I was able to identify what I thought was the offending cylinder. I swapped out coils without much effect. Then I noticed that the ignition coil connector had partially disintegrated inside, about 50% of it crumbled, and the particles were preventing the connector from seating completely. I cleaned out the connector and was able to get it to seat correctly. The intermittent ignition miss diminished. I cannot state absolutely that it went away completely, but it did occur much less.


So, the loping continued to diminish and the momentary rpm drop every 32 seconds became less pronounced. I took the car out for a drive and it did very well with only a tiny bit of loping when at stops and sometimes no loping at all. So I am not comfortable saying that the problem is fixed just yet. The XJS has thrown me curve ***** before. I am trying to source a replacement ignition coil connector pig tail so I can properly repair the connection and will continue to drive/exercise the XJS to see if the ECM will completely settle down.


Another thing that I have noticed when working this problem on the XJS, is that every time I change out a part, the ECM pitches a holy fit and the car runs horribly until it sits idling for 15 minutes or so.


I will keep the updates coming. Thanks for your help and concern.

 

Thanks for the updates on this cybercg.....

Looks like you're closing in, with the end result not far off for a final fix.
Fingers crossed, hope to hear

 

UPDATE:
So much to tell. So much ground has been covered. My last update had the XJS idling with a mild lope that would sometimes become a moderate lope and the idle dipping 150rpm every 32 seconds so the ECM could try a new fuel map. I had noticed an intermittent misfire and had found that one of the ignition coil connectors had disintegrated internally. I needed a replacement connector to hopefully address the misfire. Maybe the misfire was complicating the loping symptom. I found a 1995 XJ6 is a Pick-A-Part salvage yard in Nashville and went to visit it. Luckily the engine was intake along with the wiring harnesses. As much as I hate to cut a good wiring harness, I cut off the portion that feeds the ignition coils. After all, the connector/s will be better off on my XJS than sitting in a junk yard. While there, I also snagged a cruise control bellows, chrome exhaust manifold cover, one ignition coil that did not have a cracked body, miscellaneous other connectors, and one more part that proved to be the 'Hail Mary' for my problem. In the floorboard, where the front seat used to be was the Lucas MAF. Just quietly lying there. I figured that I had nothing to lose, so I snagged it too. This morning, I replaced my broken ignition coil connector and replaced two others whose insulation had come off the wiring. I had taped those wires previously, but could now do a proper fix. I fired up the XJS................it did not want to run and died. I fired it up again and coaxed it to life. It was still loping, but as before, the loping began to diminish as the engine warmed up. But, still not good enough. So, since I had snagged a spare MAF, I popped it in place of my old MAF. I started the XJS and it immediately began to idle more smoothly. It still had a faint loping and still would have a momentary rpm drop every 32 seconds, but the ECM seemed to like this MAF better. I had not realized it before, but I now noticed that my original MAF was NOT the one the car was built with but an aftermarket unit. Maybe it was failing. In any case, I performed the Idle Air Control Valve set procedure, available on this site, again for the zillionth time and the idle stabilized a bit more. After driving the XJS, the idle is MUCH more stable with just a hint of a lope. The lope isn't there at all times. Sometimes the idle is smooth like it should be and it still sometimes does its little rpm dip.
Is this the fix? I would certainly hope so, but it is too soon to declare victory. The idle still and a bit of a flutter to it at times and there is still the hint/rumble of an occasional misfire. I am using RC9YCC Champion plugs. I am going to try the hotter plug RC12YC recommended by Jaguar in TSB 18-56. Actually they recommend RC12YCC, but I have only found the RC12YC plug which is a copper plug with a nickel core, I think. The RC12YCC is a Copper Core plug. I have found the RC12YCC plug marketed for lawn mowers, but that just seems so wrong on so many levels.
I am hoping the hotter plug will take care of the little intermittent rumble misfire. I will keep you updated. Thanks.

 

Firstly, so so pleased that you're almost there by the sounds of it, after a lot of hard work and $$ spent.

Really looking for this thread and want to see a fix at the end of it for you.

Secondly, please accept some advice.
I really enjoy reading your posts BUT.....Longgggg unbroken lines of text are difficult to read and most members just don't bother.
Please check the difference between your original and mine above, as edited.

Just a few line breaks here n there really make the difference, so people can enjoy your posts.
Many thanks

Jim

 

I agree. The line breaks make the entry much easier to read. Will do.

I plan to replace the RC9YCC plugs with RC12YC plugs tomorrow. I will for the first time in my life, use a spark plug thread chase to clean the head threads before installing the RC12s. I have used anti seize compound on the plugs previously and want to make certain that the plugs get a good ground contact with the head.

That may be over doing things a bit, but at this point I am trying to cover all bases and hopefully win the battle.
Thanks for the encouragement.

 

We're all rooting for you!

Waiting for next installment.........

 

UPDATE:
I replaced the RC9YCC plugs with new RC12YC Champions as planned. I don't know yet if the change has helped or not. It did not hurt the progress made thus far, but the ECM did renew hunting and trying fuel maps and the lope at idle doesn't happen as much. When the lope is present, it is very minor now. The idle varies between a roughish feeling idle (like having a mouth full of gravel) and the smooth Jaguar idle that the AJI6 is known for.


I have noticed during all this that the idle is smoother when the AC is engaged. Most likely, because the ECM richens the fuel delivery a bit to compensate for the increased load at idle.


I have also noticed that if I manually open the throttle just enough to increase the rpms by 50, the idle smooths out beautifully. I wish the ECM had an adjustment that would allow the target idle to be increased from 600ish to 650-700ish. I could live with that.


An additional bonus from all the part replacements, is that the XJS is now a LOT livelier when off of idle. It was peppy before, but now it is more eager to go and is silky smooth when off of idle.


So, my plan now is to drive my XJS and allow the ECM to continue to do its thing, and hoping that the idle will continue to improve.


This problem first manifested itself about one year ago. The car had been running OK for an old car(you have to cut them some slack), and then one afternoon, it began missing and cutting out so bad that I could not get it out of the driveway under its own power. It began loping severely when it would idle. Sometimes it would not even idle. The search for a solution began.


RECAP of CHANGES: (Some of which occurred prior to the posting of this problem)

1. Idle Air Control Valve Replacement - It did not make a big difference.


1A. Performed the IAC idle set procedure many, many times - It did help a bit, but it did not solve the issue.


2. Cleaned the throttle body multiple times - No change in idle quality.


3. Tested for vacuum leaks - None found.


4. Replaced EGR valve and gasket - No change in idle quality.


5. Replaced Coolant Temperature Sensor - No change in idle quality.


6. Removed NGK spark plugs and replaced with Champion RC9YC - No real change.


7. Put the NGK plugs back in - I don't know why I did that.


8. Changed the NGK plugs for RC9YCC plugs - Still, no real change in the symptom. The symptom would vary in intensity.


9. Changed all six ignition coils with know good used ignition coils - This helped. The idle still wasn't right, but the car behaved better.


10. Tested the fuel pressure at the pump, at the rail and after the pressure regulator - All was good.


11. Replaced the injectors with a set of cleaned and flow balanced injectors - It did not solve the loping idle, but the loping diminished a bit.


12. Replaced a broken ignition coil connector found during this hunt - It did diminish the random fluttering-misfire I had noticed, but it did not eliminate it completely.


13. Replaced all four oxygen sensors - It wasn't the fix, but the car did behave a bit better. Making changes. Making tiny progress steps.


14. Replaced the aftermarket MAF that was on the XJS when I acquired it with a MAF from a 1995 XJ6 - Wow! Big difference! The loping minimized, but did not go away completely. The ECM was still trying to make sense of it all, but the idle was getting better, the car wasn't dying while idling and the car was running better at speed.


15. Cleaned the spark plug threads in the head and replaced the RC9YCC plugs with the hotter RC12YC Champions - No discernable difference - yet. I will continue to drive the car and see if it finishes settling down.


So to sum up: The problem ain't over 'til its over.


I believe that the problem was the result of multiple inputs to the ECM that had exceeded allowable margins causing it to thrash through its programming to try and bring the engine back to acceptable operating specs.


I think that the main culprits behind the problem's symptoms were the MAF and the oxygen sensors. The car benefited from all the changes and replacement parts as any 19 year old vehicle would benefit. The car is old and its components are old and many were probably originally installed when it was manufactured. I am sure that I replaced some parts that were still OK, but without a Jaguar PDU or specific OBD codes, I was operating in the dark. The code P1316 didn't exactly point to the problem and that code did not appear until I was deep into the process of trying to rectify the problem.


All told, the part's cost was about $500ish and some heartache. Some parts were new and some used that were tested as good. In today's world, most car repairs cost much, much more, so no complaints from me except for the heartache.


I will post another update after the car has been driven a while. I am hopeful at this point and the car is again enjoyable to drive.


Thanks to all for your concern and support.

 

I forgot to mention in my previous sum-up post that I had also replaced the crank position sensor. While the new one did not hurt the XJS, it did not solve this particular problem that I was chasing.


Thanks to all!

 

I have been able to achieve a really good idle after all the drama outlined in this thread and part replacements. As I mentioned earlier in the thread, the changes that made the most improvement were the MAF replacement and the O2 replacements.


The loping idle still persisted after those replacements but was much diminished. The car did not rock as much as before when idling.


The procedure that I did that finally eliminated the loping was the following.


1. Perform the Idle Air Control Valve set procedure found on this site. Using this procedure, I adjusted the idle speed as best as I could. Contrary to the IAC set procedure, my Air Bypass Screw adjustment did little to change the idle speed. I could kill the engine by completely closing the screw, but had almost no control over setting an idle speed.


2. So after performing the IAC set procedure and adjusting the Air Bypass Screw enough to achieve a sustainable idle, I opened the bypass screw in 1/4 to 1/2 increments and then drive the car around the block after each adjustment. I took a route that included a bunch of stops, so the ECM would have to return to an idle after running the engine off of idle. I recorded the bypass screw setting each time and then recorded the results.


In my case, after opening the bypass screw a couple of increments, and driving, I noticed that the loping had diminished a bit. I continued opening the bypass screw in small increments and driving after each adjustment. The idle speed began to respond by increasing and the loping continued to diminish. After a few iterations, the idle speed had increased to between 600-625rpm and the loping had almost completely vanished. Yay!


I continued to drive the XJS over the next couple of days. The loping has not returned. The idle is pretty solid at 600rpm and the car no longer dies randomly at stops.


So, the air bypass screw does make a difference. It along with the MAF and O2s do seem to be critical to a stable idle (among many other factors).


My idle is now as smooth and sometimes smoother than the idle on our XJ8.


I hope that my experience can be of help to others.


Thanks to all!

 

Superb, so glad to hear, I was looking for this post and was wondering.

Glad all is now good



Jim

 

Fantastic narrative. This will undoubtedly be very valuable to others in the future.

I appreciate your willingness to return, over and over, with details on attempts and it's effects to the problem.

Last question, what was the car idling at before you started monkeying with the bypass screw?

 

The idle varied in the 500-550 rpm range before I tried opening the air bypass screw in increments while the Idle Air Control Valve was connected. . Based on the outcome, the engine was being starved for air. That isn't what started the problem, but was the last piece of the puzzle. I am relieved that this problem is now behind me. Thanks to all!

 

I wanted to let the forum know what the final setting of my Idle Air Bypass screw was.

Two and one half turns from fully closed was the setting that my ECM liked the best.

I am sure that this may vary a bit from car to car because there are so many variables in play, but it could be a good starting point and a time saver.

 

Where is the air bypass screw?
Thanks, RagJag