Hi Gents.

I really hope to get some pointers here as this is becoming a real nightmare. Not as much for the problem itself, but rather for my vivid imagination of all kinds of destruction that may follow .

JagX exhibits following symptoms. It all begins after he warms up and comes to stop at red light/stop sign. Idle is stable at first and then comes the first stumble. What's really peculiar is that there is absolutely no indication in terms of rpm drop or warning lights in case of this problem. The frequency of the stumble is rather erratic with no predictable pattern...sometimes all I get is a smooth idle. Here comes the cherry though. If the stumble continues recurring more frequently than I can handle, all I need to do is simply slide the tranny into neutral and all is smooth...

There are absolutely no codes, the car starts swell, and also drives good besides the aforemetnioned problem. Perhaps I should also mention that when in park, after warming up I can occasionally hear very deep, random thumping knock

Thank you in advance for any suggestions on how/where to begin troubleshooting this .

Best,
Danny.

 

Does it stumble at all when accelerating hard?

For most things the error has to occur multiple times within a time window for the light to come on. If you've got an OBD reader you can also check pending codes, which are things that the ECU saw, but haven't reoccurred recently enough to set the light. Might give a clue.

 

Shine a bright light on the BELT tensioner and see if it is visibly jumping when you hear the thumping in Park. If it is one of your idler pulleys or rotating accessories probably has a bad bearing.

 

@ ccfulton: Oddly there is no stumble or slipping during hard acceleration, driving, or down the hill free (foot off the gas) glide with tranny properly downshifting as needed... I have Innova 3100 which I strongly believe does not provide pending code option (it was a right price though ).

@ WhiteXKR: What a fond suggestion ! I will take a look at it throughout the week. Hope you're right, mate! Would be much cheaper fix than rebuild job on my still sound feeling transmission.

Thank you, gents, for the ideas. Will report back soon!

 

After careful examination and cleaning of air induction components along with MAF sensor, getting resistance on injectors + BG44K in the tank, it all came down to the spark plugs...when I got to coils I noticed a bit of rust on the exposed metal which I brushed off and wiped over with almighty WD-40. The spark plug wells were not necessarily filled with oil (which would point to valve cover gasket), but sparkplugs looked much worse then the picture below that I took about three months ago when troubleshooting a starting problem. All had hardened crud over them which could not hold up to dual strength wire brush scrubbing. Next I dried them all off, wiped the threads with WD-40 and put it all together...Go figure, JagX is back to smooth idle. So my bottom line here is, if you do not get codes yet have idle rough enough to be alarmed then take a good look at your spark plugs. Btw, mine are NKGs and were put in last year in March .

 

Have you had any recurrence of the problem?

I am having the same issue with my 2000 xkr. New plugs about 1000 miles ago so I haven’t checked there yet. Car was parked for nearly 2 years before I got it. I put on new jag coil packs and new plugs.

the problem isn’t always there

 

Sometimes it is the throttle position sensor. The area of the sensor for idle is the first to deteriorate since it rests there most of the time. After sitting unused for a while this area of the sensor is further damaged.

 

Thanks I will check that out. Easy enough to change

 

Please be advised that you will need IDS or something similar to calibrate it.

 

thanks. I’ve read about the hard reset. However, I am trying to find an IDS. I have a computer etc that I use with FORSCAN in Fords. Now I’m on the hunt for the Jag software. I relatively new to Jaguar

 

Turns out my problem was a faulty mass airflow sensor. Bought a new oem sensor and housing.