I've got about 28k on my 2011 about 3k ago started to rough idel. RPM fluctuates up to 2300 when in park. Car also seems to be missing every once in awhile, like a bad plug. Also when coming to stop light seems like a very hard down shift from 2 to 1. My wife always looks over at me like why am I braking so strangely.

 

This is NOT normal cold or hot.
My new 12 XKR is still in service for this issue going on three weeks and according to the shop foreman it's either valve guides or a cylinder head issue requiring a new head or replacement engine; the dealership had been speaking driectly with and sending data to Jaguar engineers in the UK for weeks. It appears some 11's and 12's (so far) have this issue. Do not ignore this issue thinking its okay if it goes away when warm...my car did the same thing and my car had NO check engine light. Jaguar is buying my car back.

Best of luck with this issue hoping it turns out to be something minor.

Here's a link to my thread https://www.jaguarforums.com/forum/x...10/#post512465

 

So, do you see RPM changes while idling? I'm just trying to figure out if my cold idle feels 'normal' (this thread has me worried). When cold, every now and again, it feels like a light "push" on the car, probably every 20 seconds or so. Doesn't perform rough otherwise, nor do I see any major fluctuations on the tach. I have a 2012 XJL S/C, and have not put anything but premium Chevron / Shell fuel in it. It has 900 miles on the clock.

 

Mine stumbled/twitched ie misfired during the cold start cycle but intermittently from week one and no check engine light came on. My car smoothed out when warmed up fully. I originally thought and hoped it was just a bad tank of gas but after trying four brands/tankfulls with no change I knew something was wrong. At first the dealership tried to tell me if there's no light then there's no misfires but after I returned again the shop foreman explained that there has to be a certain amount of misfires over a given time for the light to come on; after they hooked up my car to their diagnostic equipment and started it each morning they found the misfires. Hope this helps.

 

I guess I don't know what a misfire feels like...

 

Kinda like your engine skips a beat or stumbles causing the engine and car to shutter.

 

The Jaguar supercharged engines do not run 100% smooth when cold--every SC'd Jaguar I have owned did this and it should be of no concern. It is a very slight off/on hesitation that completely disappears when the engine is warmed up. If this continues after warm up, then you have a problem that needs to be addressed. Otherwise I would consider it normal. I believe a couple of Jaguar techs have confirmed this on the forum.

 

It should be easy to tell if your car has a normal slightly lumpy idle or a misfire as the mis is a sharp severe jerk like the engine is being starved for fuel for a second the immediately starts again and repeats this with every misfire. My dealership was easily able to see the misfire on their diagnostic equipment and it wasn't normal. Hope yours turns out to be something minor.

 

Recently, wife and I have noticed vibrations on our 2012 S/C when the engine is cold. This vibration disappears after driving for 5 minutes and does not reoccur (say we park and then restart after 1-3 hours same day) hence I cannot show it to a mechanic. But last weekend, we did not notice any vibration (the garage valet guys moved the car near the exit of the garage and the weather was warmer compared to 2 weekends ago)

We typically drive once a week and rest of the days, the car is parked in NYC garage (almost 2 months, less than 500 miles). Also, before driving the car esp in winters, I wait for the rpm's to drop below 1500.

Should I get it checked up or wait and see?

Thanks,

 

If its a sharp quick twitch like movement in the engine enough to shake the car and that happens randomly during the cold start cycle then yes. Also the very mild lumpy idle that some are referring to would be rather constant until it warms. I started my car many times cold and the idle was perfect no lumpy idle at all and perfectly smooth. My car had to sit overnight for the misfire to occur, 1-4hr restarts were ok. Hope in your case it turns out to be nothing.

 

Apparently BG44K is used as a first resort to fixing this, I heard.

Has anyone used this stuff?

Also, what kind of gas mileage are you guys getting on your S/C engines? I went from the normal engine getting around 18 city / 28 hwy to the S/C and get around 15-16 city / 23 hwy. Does that sound right?

 

I'd suggest adding a bottle of octane booster to as full tank of fuel and see if your issue resolves itself.

Sometimes the quality of the fuel causes this. This has also been documented, especially with the changes in fuel blends such as when the season changes. Also, some places where you purchase fuel could have contaminants in there tanks.

 

I get 10 mpg in city (remember I live in NYC where one has to deal with kamikaze pedestrians, crazy cabbies, etc) and roughly 22-23 on highway on my s/c.

 

My recent trip to the dealer for the engine jerking resulted in another can of BG44K. This will be the second treatment. I had the service manager come sit in the car where I demonstrated the engine jerking, like a misfire.

We both agreed that a little variation in RPM at idle is normal. But then we both felt these intermittent jerks. He said he had not noticed these before, but now knows exactly what my concern is.

I still don't understand or believe how a can of fuel additive can fix this problem. First of all, the fuel additive won't even get above the valves due to the fuel injection location. Second, we don't know for sure what the problem is. Third, why would a brand new engine with less than 1500 miles on it have carbon deposits severe enough already to cause engine problems. Fourth, why would fuel injectors be dirty already. Fifth, modern engines should be designed to run on commonly available fuel, not just one specific brand. That's why we have fuel filters, moisture evaporators, etc. Sixth, just because all previous Jaguar engines have had a rough idle doesn't mean that a modern SC engine should have the same. Seventh, forced induction does not have any inherent reasons to cause either a rough idle or engine jerking, especially when fuel injected. Eighth, high output engines are not necessarily prone to engine roughness unless you have static valve timing, limited ignition timing, and a traditional carberator. The SC Jag has none of these.

Jaguar has some work to do on this issue. It is definitely not normal, shouldn't be related to carbon deposits or dirty injectors, and should not occur by design.
I personally think it is related to valve and ignition timing under certain conditions processed by the ECU.

I will see if BG44k helps, but I didn't purchase a 90K car so I could continue to add a $40 can of fuel system cleaner every 3 months or 1500 miles.

 

I consistantly get 18 MPG around the city with a mix of freeway & street driving. I have gotten upwards of 24 MPG on the highway.

 

Teachdocs

You're right about the necessity of fuel cleaner on a brand new car let alone multiple treatments; it sounds like you may have another issue similar to mine; what is the production date of your car?

 

Almost every s/c xj I have driven/worked on from brand new have a slightly rough idle. The direct fuel injectors are in the combustion chamber and are exposed the the carbon deposits. Have been occasionally been replacing injectors for misfires. But to get to the point of replacing, jaguar wants us to do a fuel system cleaning first to see if tue misfire codes return. Then if they do we replace the clogged injector. The openings on the tip become plugged with carbon. Even though the are operating over 1000psi the still are getting clogged causing an improper spray.

Some roughness at idle is normal but if it is setting a check engine light it needs to be addressed. most cases you are gonna get a fuel system cleaning and then you will be disappointed because it still shakes a little at idle. It also wouldn't hurt to open it up once and a while to clean out the build up of carbon.

 

This is going to sound crazy, and it might be coincidental, but switching from Chevron to Shell gasoline seems to have helped my weekday morning idle shudders... We'll see if it had an effect on the 2 days without driving shudders on Monday morning (which seem to be the worst of the bunch). I like the "open it up once in a while to clean out the build up" idea... This car is so much fun!

 

The problem I had was far beyond a rough idle and verified as misfire numerous times by the dealership and Jaguar USA. I was at the dealership yesterday and was told my former car would be getting a rebuilt engine with the original engine being sent back to the UK for for further inspection etc. The problem so far was traced to a defect somewhere in the cylinder head(s).

I tried changing gasoline several times all to no avail.

Hope this helps.

 

Would all misfires trigger a code on the OBD-II diagnostics? I hooked up a wifi dongle to my OBD port and had it read codes after startup. Nothing triggered a code.