2007 XK 4.2 130k miles
Engine has recently begun “hunting” when driving along. OK for first half mile but then engine revs vary up and down by about 50 either way and speed rises and falls with this. Noticeable hesitations in acceleration. New air mass sensor was suggested remedy. First one made it much worse. Second one got it back to the same place…….still hunting. Continues hunting when on tickover in Park, but no hesitation under full acceleration. Lots of hesitations under gentle acceleration. All suggestions gratefully received!!

 

Has the car been checked for vacuum leaks?

 

Make sure your intake boot hasnt slipped out of place. If your motor mounts are toast, the engine movement is enough to dislodge the intake boot from the intake snout.

 

My engine mount broke and tore the holy hell out of the intake piping.

 

Welcome to the forums Mjyfly,

Throwing parts at a Jaguar is a slow way to troubleshoot and fast route to poverty.

Air leak is the number one suspect for this symptom but a code reader is your best friend. Not all faults set the MIL and you could well find something in stored or pending codes to indicate other possible causes.

As you have posted directly in the Model forum without first posting an Intro, please read guidance for new members ( https://www.jaguarforums.com/forum/n...ned-up-241802/ ) which answers many of the most frequent questions about getting started.

Graham

 

Thanks Graham for your guidance and I have modified my signature as you request.

As a newbie to this type of forum, I was not aware of the etiquette. I have tried to post a brief intro as you requested, but had some difficulty finding where to do so. This may perhaps be because I use an iPad not a PC. A link button from the headline would be useful for beginners like me! Thanks also to all those other members who have so far added their suggestions. I shall certainly be exploring these as soon as I can get access to a code reader.

 

You have an old car. Actually, we all do. Performing a Vacuum Leak Smoke Test would be a prudent thing for us all to do once in awhile.
SO, maybe get a vacuum line smoke test done. They are quick, easy and fairly inexpensive to have done, maybe $40 or so.

 

Buy an Autel AP200 with the JLR software (or equivalent, if it can read JLR codes and live data). Plug it into your OBD and get comfortable with it. $70, for your IoS or Droid.

Test your Long Term Fuel Trim, noted as LTFT, on both banks. An air leak (or sometimes called a vacuum leak) will cause the ECU to try to compensate for the extra air in the system. LTFT should hover around 0%. More than 8% plus or minus or either side means you have a air/vacuum leak. Then do a smoke test. Avoid throwing parts at it.

 

My thanks to all who suggested an air/vacuum leak. Garage had come to the same conclusion. It was due in this week for a new brake servo and some of the lines were leaking. All good now.