Misfire what misfire... I had a MAF sensor needing cleaning, Jag dealer had the car for 3 days and was unable to sort it, it cost me 3$ for a tin off carb cleaner, and the problem went away. Unfortunately its difficult to find a mechanic in the UK that's is able to understand these complex systems, no fault code seems to mean nothing wrong. Bring back basic skills.

 

All too common to find UK people who have not a clue about the basics of a computer-controlled engine (despite it being decades now) and thus no clue about things as basic as a MAF.

OBD is a mystery to most, too

 

Nice try but largely seems false!

An air leak can and often does that, yes. Look at fuel trims with OBD live data to see. Spray something safe but burnable like MAF cleaner and watch the trims change if you get to the faulty area.

 

One of the best thing about these forums is that you can compare your problems with others who suffer like symptoms. My 2004 X350 idles low and sometimes a bit rough... Reading this post convinces me that this is just an ongoing problem that most likely won't ever be resolved. It is supposed to run this way, I guess, so I'm just going to accept that newer cars don't run as good as the older ones, and just live with it.. Buying a newer, low mileage car won't be a move up, and therefore not really to be considered... Brandon

 

Simple idea and brilliant thanks

 

I did not read all above but I have the understanding.
They cleaned everything ? Checked everything connected to the problem?
Changed the plugs? Did they check the condition of the plugs the second time around?
Gas is top of the line? 92 or above? No water was found in tank? No oil or water in gas?
Just gas??
HOW COULD THEY NOT KNOW? It makes no scene. What have they changed for observation? If they have no idea then parts should be changed one by one till the car starts running correctly..........................I would Get a Lawyer!! There is more to this then we are seeing and or hearing. As far as I am concerned, these are not actions of top Mechanics.

 

I just test drove a 2012 XJL Supercharged. It had the misfire issue.

It's pretty bad. It wasn't so irritating during the test drive, but I could see it being a major problem if I had to live with that every day. It just feels like uneven idling and jerkiness when idling. My 4.2 XKR does not exhibit any of this behavior!

 

Dicing with "famous last words" but my STR also doesn't have apparent misfires.

 

I have been having a rough idle lately in the 2006 XJR. Thinking I may pull the plugs and re-gap them. (it felt rough before my tune up off and on, but now its regularly rough idling) Would the rough idle be caused by a poor pre-gapping of the spark plugs? Or possibly a bad MAF sensor....

 

How did I get in this x351 Forum... Sorry for the wrong placement.

 

If they're iridium plugs like the STR uses, don't even try. They're very delicate and anyway good for 100K miles. Just replace if old.