I just purchased my 2012 jaguar xjl portfolio 5.0 a month ago it has 41k original miles on it. When I first got it I would barely press the gas and it would just literally float like a butterfly & the sound coming from the exhaust was the most pure sound. You could hear those intake manifolds opening up justtt right. Now there is a lag when I press the gas it literally takes too long for the car to register the fact that I want to accelerate at that exact moment. The sound coming from the exhaust is now more so on the raspy side it doesn’t sound pure at all anymore & I hate that!! It’s sounds almost as if I am driving on air and not gasoline I want that purity of sound back & to have my engine purr again like the pretty kitty she is!! Any idea as to how this happened and what to do to fix it?

 

Eli, not to question the conditions of the car, but are you putting 93 octane (91 RON) in the car or are you using a lesser octane gas? If you are going with a lower octane gas, that may be what you are experiencing. Also, as some members will attest to, these cars can be picky as to what brand of gas you put in them. If you do a look at "top tier gas stations", you will be able to find one in your local area and I would say to give them a try to see if things go back to what you are thinking they should be.

After this, I am not sure what to tell you. part of me is going "you have a problem, just not sure what it is", and part of me is going "is he just getting past the initial new car excitement and the car is operating the same as it ever has". I tend to go towards the "there is a problem" side, but I am not sure what it could be. I am doubting that it is exhaust related unless you got a really bad tank of gas since you have bought the car and you have somehow clogged the cats (I find that hard to believe, but is a possibility).

Hopefully some other members can chime in with some ideas.

 

That is a nice low-mile 2012. Congrats.

Its hard to know if there is a problem there or not. I would generally recommend changing your air intake filters and cleaning your MAF sensors, as it is cheap and easy. Getting good gas is also always a good idea.

If you need to diagnose further, grab an OBD scan tool and see if there are any pending codes. For fuel/air mixture issues, you can look at fuel trims using a scan tool too. If you don’t already have a scan tool, ask for recommendations as they vary widely in what they can do. Personally I use a combination of the iCarsoft LR v2.0 and a BlueDriver wireless scanner. The iCarsoft does everything when I need to do a deep-dive, the BlueDriver is much more convenient and user friendly and therefore remains plugged in > 95% of the time.

 

Def using 93 octane at all times as recommended! I will def give that “top tier gas stations” search a try. I usually stick to chevron, shell, etc. Maybe my knowledge isn’t as up to par as I thought. Will give that a shot though !

I feel as though it’s minor of course I’m no mechanic but even as I type this right now with my car in park my engine is shaking almost as if it’s throbbing. Maybe some sort of fuel lines or ?

 

Always diagnose in the order of simplest/cheapest potential problem first. What can cause the symptoms you describe? Well, lots of things, but the simplest/cheapest is likely a vacuum leak. Open the hood and inspect all of the plastic piping between the two air cleaner boxes going back to the throttle body and any tubes or other fixtures attached to it or to the intake manifold (or any tubes that look like they used to be attached to something). Any cracks or broken or loose connections will let un-metered air in, thus degrading performance, even very likely making the engine run so poorly as to shake at idle, plus a big enough leak you'll be able to hear the change in the sound when you accelerate. Lets hope its something as simple as a loose band clamp.

Beyond that, the next cheapest thing to do is to check for diagnostic trouble codes stored in the computer as Nick suggests. You may not own a scanner or wish to buy your own, but generally many auto parts stores will be happy to read the codes for you for free in the hopes that it will reveal some broken part that they can sell to you. Then post back the trouble code numbers and someone on here will likely have further recommendation.

 

Rubber hoses under the hood dry out over time and can crack. A pinhole in a vacuum line can cause the symptoms you describe. Don't waste time trying to find that needle in a haystack. The best way to find it is with a smoke test.

Here's how the pros do it:
https://www.tomorrowstechnician.com/...a-vacuum-leak/
Or search YouTube for DIY smoke test videos.

 

Reminds me of some issues I had on my XK8 and my XKR (X100): after some time driving only in town and traffic jams the ECM did become « lazy » and the car less reactive as it auto-learned slow driving patterns. Solution was to drive a long time on highways at high speed, or reset the ECM by disconnecting the battery.

Not sure this applies to X351, though.

 

That is exactly what is happening as I am sitting here typing this response my engine is literally shaking every now and then at an idle. Some times more aggressively than others ! Could this cause an issue as I am driving as far as the transmission is concerned when switching gears ? Seems like every week it is shifting harder than the week before..there’s also a drag in the response time as far as shifting goes. It’s very abrupt as I go into each gear making the ride very uncomfortable, I can feel it going into 2nd, 3rd etc almost as if it were a stick shift!

 

I am most likely going to have to take it to the dealership to get it fixed. This seems to be the problem though ! You guys are awesome with the responses !

 

I too only drive in town & rarely any traffic! However I know for a fact that I don’t drive the same as the owner before hand & May have put a lot more stress on the engine than the driver before hand... Maybe the issues are now becoming prevalent because of that ?!

 

Our OP didn't sound like was going to get that deep into the weeds with diagnostics but for anyone else considering serious DIY automotive diagnostics, I bought for detecting leaks. Its a pretty slick little tool and its saved me some headaches. You kind of need to be familiar with how all the plumbing is routed and how the various vacuum subsystems are supposed to function so I wouldn't recommend for the average DIYer. I bought it because I have been dealing with vintage Corvettes where virtually everything is vacuum operated and designed by Rube Goldberg himself. This is the kind of specialist tool you get after you've already got a giant rollaway tool cabinet full of mechanics hand tools. There's also DIY instructions on the web how to make one of these smoke testers yourself, but you could spend a lot of time gathering parts and whole weekend building one so the cost to just buy one already made seemed reasonable.