Facts, 2009 SC XF, 51k miles. First, I'm having an erratic, intermittent idle issues, where it will fluctuate between 500-1000 rpm once every 2 seconds. No rhyme or reason when it does. So far it only has been occurring in park. Is there some kind of idle unloading valve for the supercharger ? While stopped at lights, it will vary between 500-600, and I can feel a steady vibration that goes away once the rpms increase.

Twice in the last week, the engine has died, once in drive, once in reverse, cold engine (well, its already over 100 deg in this part of the world).

Secondly, in the last few days, there is a hesitation between when I press the accelerator off of idle, and the engine responds. Its such that I press harder, then get hit with more power than I wanted. There seems to be an overall decrease in throttle sensitivity as well.

I have not taken it to the dealer yet (headed there in another 18 hours or so), but I don't have any real faith in the techs in this part of the world to do real troubleshooting, so I'm asking here to get an idea of what I can tell the service rep to have the techs look at beyond what they normally would.

I'm going to ask them to put the code reader to see if any codes come up, check the air filters, and clean the throttle body at a minimum. This country is a very dusty desert, so I'm hoping that is something related to that.

Any other suggestions would be greatly appreciated.

 

Although I have no specific experience with that engine, it sure seems like the throttle body or TPS would be a likely place to look. Do the techs you use have Jaguar specific diagnostic software? If they do not, I suggest you consider buying your own.

 

It sounds like you have a small vacuum leak. Normally you would get a check engine light but maybe it isn't bad enough to trip it. The Jag techs on the forum stated there is a known issue with a rubber line that becomes brittle and falls apart on the 4.2L supercharged motors.

 

The fault is described as being under the intercoolers me a bit@h to fix so might not have been under warranty. Which would be a shame. Air leak downstream is a common cause of idle problems.

 

Thanks for the info guys. Its at the dealership now, and I instructed the service rep to have the techs clean the throttle body.

When I first test drove the car, it had an idle problem just like it does now, just a bit worse. The owner had several hoses replaced (he gave me the receipts from the dealership), and it ran perfect when I bought it.

The rep also warned me that he has had recurring problems like this with US spec cars in this country. He had a US spec XJ come through a few months back with similar problems, and they replaced the cat converter.

I'll call the service rep and tell him to have the techs check all the hoses for condition and air leaks.

 

Service reps saying its a bad catalytic converter... How in the hell does a cat converter affect idle speed? Also, the tech found a non-standard breather hose. Not sure what that means other than its not a Jag OEM part, but that sounds more likely, and a lot cheaper than having to pay the astronomical dealer markup on parts ie. $1000 part in the states will cost double that in this country...

 

There is a downstream O2 sensor after the cat. If that were the problem, you likely would have a smooth idle when the car is cold and you first start it up which becomes rough once warmed up and the system is using the O2 sensors to adjust the fuel.

I leaking breather hose could very well be it though. A small crack or bad seal may only leak enough to be noticeable at idle RPM.

 

If you want to drive a jaguar of any age, in any part of the world, and the price of service matters to you, then you need to get set up to do some level of service yourself. And to me, that begins with a way to read codes and paramaters.

Otherwise, just consider dumping a few thousand a year into the dealership as a cost of ownership.

 

Got it back today. Most useful information I got from the report was that the wire harness for the O2 sensor appears melted. Didn't say which side (if there is one on each side). Also, there is a "modified" spark plug that needs to be changed, so that means to me replace all of them. The non-standard breather hose is on order. The report want On to say that there is wear to the honeycomb in the cat. I'll have to read the report again to see which one it mentions. The throttle body cleaning was the only actual maintenance that was performed to remedy the idle problem. As of right now, it idles smoothly at about 650, no fluctuations so far. I do plan on working on the car myself, but this country is not really set up for the DIYer. I'm a helicopter mechanic, so I have the ability to do small stuff once I know what the problem is. If I can reach the burnt O2 sensor, and figure out how the wiring harness is routed, I should be able to do it myself .