My new (to me) 5.0 XKR seems to have a slightly rough idle, almost like a small misfire every few seconds or so. It's like the engine rpm dips noticeably but very briefly, not enough really to register on the gauge on the dash but it can be felt and heard. I checked the oil level just after I got the car, checked recently and it seems to flit between halfway and MAX on the dash so I'm guessing the actual oil level is sitting just about the point where the system would register a drop from the actual maximum level, so maybe use 0.3L in 1000 miles. That's within normal usage limits according to the manual but given the slightly rough idle I'm wondering if there's an issue? PCV springs to mind, any idea how accessible that stuff is on the 5.0 S/C? Anything else that could cause this?

 

I would start at the injectors.
Do a professional injection and intake cleaning service, it needs it regardless.

One other thing as safety and maintenance.
Have someone else start the car, note if you hear any unusual noises that dissipate after 5 seconds of running.
What you are looking for is a failing cam actuator.

 

Thanks. You mean like Terraclean?

 

Yes. Its absolutely worth it- in just the performance gains.
How many miles on your car.

 

"only" 47k but it is 9 years old. There's a Terraclean agent not far from me, I'll try them.

 

At 47k its slightly overdue.
Do the GDI service and the Injector service.
You will need to change the oil after you are done.

 

OK so is that a Jaguar-prescribed service item then? I don't recall seeing it on the A and B service check sheets? Can you elaborate on what "GDI service" means?

 

Its not prescribed because in a decade ago they were both unaware of the problem and the fix did not exist.

GDI stands for Gasoline Direct Injection.
After a few years on the road, an inadvertent byproduct of this new technology was realized.
The valves were getting extraordinarily dirty (Jaguar is somewhat exempt from this due to design, but not exempt)

See the issue that many dont realize is that a GDI engine is not just producing carbon, its producing an exceptionally hard form of carbon.
Here is a great test done.
https://www.enginebuildermag.com/201...-fictions-gdi/

 

In the GDI service they will just run cleaner through the intake.

You can do this yourself too if you do your own oil changes and such.

 

Ah ok, just when you said "at 47k its slightly overdue" I thought you meant there was some sort of service item for having the intake valves and injectors cleaned, if not by Terraclean then by some other, perhaps more rudimentary means.

I've contacted the local Terraclean agent, waiting to hear back.

 

You wont need the rudimentary method.
GDI service is just something you should do while you are having the injectors cleaned.
And for all we know their service might come as a package- intake clean and fuel system clean.

 

Yes at 47k miles there is a strong chance the injectors are under-performing, depending on if cleaners were used prior.

 

You mentioned "new to you " Jaguar so when did you get the car and was it like that when you took delivery. If we are talking less then a month I would go back to who you purchased the car from and discuss having them look at it to see what the problem could be. Oh they should pay for the diagnosis.

 

From what I can make out the car has only ever been serviced at Jaguar main dealers so it seems unlikely that anything like that will have been done.

Bought the car two months ago and the dealer is the best part of 400 miles away. I only noticed this in the past week or so.

I hooked up my laptop with SDD this evening and had a look around, didn't see any trouble codes relating to poor idle. I reset the ECU adaptions anyway, will see how the car is tomorrow while I wait to hear from the Terraclean people.

 

Engines newer than 1965 or so reburn any combustion byproducts through the PCV system. Sadly the oily air is ran back through the intake tract and it clings to everything aftercoolers being the worst recipients. On a conventional intake port injected engine the injector sprays fuel onto the closed intake valve which washes it off. Closed because they found the hot valve helped vaporize the fuel better. The intake valve on direct injection engines do not get washed so the oily muck bakes onto the back of the valve restricting airflow. The 5.0 does have a very intricate oil recovery setup on one of the valve covers that does a pretty good job of scavenging oil from the air. However it still builds up on the intakes. There's an interesting read in the 5.0 service manual.

 

Thanks for that, I had an idea what the issue was but not to that level of detail. When you say there's something in the service manual, are we talking about the big, like 4000 page PDF document? One thing I didn't see in the workshop manual was any instruction as to how to go about removing the PCV components, are they integrated into the camshaft covers or can they be removed independently?

First drive this morning after resetting the ECU adaptions last night - don't want to jinx it but I didn't feel anything like misfiring today, idle (even once it settled down from fast idle to normal) seemed smooth and even. Totally not expecting it to be "cured" just like that but will monitor it and plan to get the Terraclean done anyway.

 

So a day or two later I now get very occasional "hiccups" (I guess they're not real misfires as there are no codes telling of misfires) but not as much as before.

Someone on another forum I posted this on reckons the problem is with the cam chains or tensioners and said I'm looking at a large bill to put this right. I'd have thought an issue like that would be noisy and probably also throw codes (seen timing error codes on previous cars before) so it seems a bit premature and drastic to suggest that at this stage, would that be right?

 

I would guess that chains/tensioners would exhibit a more consistant condition rather than the occasional ones you now describe. As suggested above, I''d endevor to have the injectors and intake cleaned to see if that makes the symptom go away before guessing at other possible causes.

 

Mine does it as well but usually only in the first 5 minutes while warming up. There is one particular set of traffic lights a couple of minutes from home where I wait to turn right on my way to work where it does it pretty regularly.

I thought I was going to stall the car the other night when I went to the mall and they were controlling traffic in to the car park due to the Xmas shoppers. I was stopped on the ramp and only had 18 miles worth of petrol left and the idle got decidedly lumpy, I assume due to the angle the car was at!