Guys, I'm pulling my hair out trying to figure out what is causing this lumpy idle issue. It's a '96 XJR with 117k on it. Maybe you can help.
First, a bit of what I've done already: New supercharger (done by the dealer), all 6 coils replaced, new plugs, new fuel filter, new cam cover gasket (along with upper timing chain tensioner), cleaned MAF, and ran 2 bottles of Techron through it.
Power is good and smooth. Idle seems pretty good in park or neutral, but the lumpiness is noticeable when idling in gear. It also seems exacerbated after driving a bit spirited.
Before some of the work was done it has thrown codes P1138 & P1158 and this has only happened twice since buying the car in April.
Any ideas here? I'm moving across the country soon and would like to get the big cat sorted before I make that drive.

 

I'd be suspicious of the new coils.

 

Care to elaborate? It had this issue even before I replaced the coils.

 

See the massive coil thread, no time to find a link, but its bound to be on one of the first three pages of threads. "New" is no guarantee of "Functional"


Maybe also want to look at a recent thread where someone has a problem with #3, and it may possibly come down to the specific #3 cyl firing circuit.
Sorry, can't recall the title, but it is quite recent and likely on the first page.
Engine ground strap would be another thing to check.
Is it lumpy in 32-second intervals? See Razorboy's lumpy idle thread

 

Here is a link to my thread about the ground strap.

Remember that I already did the ground strap once and had to do it again so just because someone may have cleaned it up before doesn't mean it isn't causing issues again.

My XJ has been bulletproof since I fixed this with smooth idle, no dip, no lumpiness. Worth checking as its stupid simple.

You can do an even quicker test just by using a set of jumper cables to present another ground path from the engine to the chassis.

https://www.jaguarforums.com/forum/x...-strap-152174/

Bernie

 

Thanks guys! I'll check those out. Start with the simple items first and work my way from there.

 

To elaborate on the coil question, what brand coils did you put in? Most bad experience has centered around cheaply made aftermarket coils, and there are only a few suppliers whose coils have proven to be trustworthy (Eurospare, Denso, Airtex/Wells, perhaps some others). Also, are you experiencing any stalling issues at idle?

 

Not sure of the brand, but I bought them from Coventry West. No stalling whatsoever. Just an intermittent lumpy idle.

 

cleaning the fuel injector and the fuel rail will help ease the uneven idling. check the fuel pressure of your fuel pump.

 

Well, the problem persists. I removed and cleaned the engine ground strap well and poured in some more Techron. I'm going to inspect and probably change the spark plugs again tomorrow. If I don't find anything obvious during the plug inspection, I'll pull the injectors and have them cleaned.
On the downside, I'll be without my Jag for a couple months while I'm in MA and I probably won't have time to get to the injectors until I get back.

 

Brad:
I preface this advice by telling you that it seemed unlikely to be accurate to me, but it has been reported by many credible posters on this and Jag-lovers - that using the original recommended spark plug part number and brand has fixed lumpy idles. I have always been of the opinion that specs is specs and the ignition system should not be so sensitive to brand to brand variations. I would make sure the gaps were set on the low end of specification to keep the coil firing voltage lower.

You did not mention what your fuel trims were doing. So that begs the question of whether the rich codes were "flyers" or if the car is regularly running rich. Being on both banks, I would suspect it is actually a valid code and you should look more there. Also, did you notice the question about a 32 second period for the stumble? There have been reports that seem to indicate the fuel maps are reset at an exact 32 second period.

BTW, from one of your previous posts, you questioned whether the rich codes were from the misfires. Remember that a misfire leaves the oxygen unburned and the sensors are oxygen sensors not combustibles sensors, so counter-intuitively, a misfire will give a lean or high oxygen reading. I keep harping on that in order to try and help you get your mind around whatever relationship might be between your codes and your misfire. Or maybe they are not related at all!

 

I'm currently running Champion RC12YCC gapped at .035".
As far as the 32 sec thing, it doesn't misfire during those intervals. It seems random, but is definitely more noticeable after a "spirited" drive.
The CEL codes it's thrown have been a mystery to me. It's happened 3 times during 7 months. The only time I notice rich is during a cold start, but that's to be expected. I may hook up a scan tool and get some readings today.

 

The first "quick test" you should do with the scan tool is determine the STFT and LTFT on both banks at idle. If your scanner records trend charts, then get the same 4 readings while running it hard. Then watch all 4 during transition back to idle.

You want to see to see several things- How much trim is being applied normally to be sure your O2 sensors, MAF, temperature sensor, and intake plenum are OK. You might even see something to indicate the injectors are not balanced,but that is harder.

I doubt it is little consolation, but many of us have had elusive lumpy idles in X-300s. Not bad enough to stall, but just bad enough to be very annoying sitting at a stop light. I hope Doug chimes in here soon. In my case, the lumpy idle was accompanied be occaisonel fast idle and I really do not know which thing I did trying to fix the fast idle also fixed the lumpy idle. FWIW, changing and calibrating the TPS fixed the fast idle, but the CKPS, plugs, boots, MAF, and probably some more got changed along the route.

I think your idea to have the injectors cleaned and flow benched is a good next step.

 

Sorry for the late reply. I've been busy with work up in Cape Cod. I really appreciate the help. I did take a stethoscope and listened to the injectors. A couple of them didn't sound quite like the others.
Hopefully I'll get a chance to spend a little more time working on it when I get back to Alabama. It's looking like I may only have a week back before relocating again (without the Jag again).
You guys know of any trustworthy places to send the injectors to?
On a side note, it's only been 1.5 weeks and I'm already having withdrawals.