I've been sort of bouncing around the forums with various posts as I try to eliminate this cars lumpy idle on my 86 XJ6 (california car). I would love if any of you had any more suggestions/thoughts.

I've spent a pretty serious amount of hours researching this and jaglovers regarding idle quality. I've even ventured into other sites that share our fuel injection system.

As many have encountered, these cars can run great throughout the rev range, but with a suspect idle quality. Ever so slight missing detectable only at idle and slightly above. You can note slight puffing at the exhaust.

Some background, this is a 44K mile rust/corrosion free car, well serviced, and garaged. Car starts almost instantaneously (thanks to Pertronix). Even the rubber parts I'm replacing are still pliable for the most part.

In summary, this is what's been done to date:

As I've recognized the number one issue regarding these cars is air leaks, I've replaced all vacuum lines/AFM bellows/Cruise Bellows/Breather pipes/Coonskin Breather top, including any vacuum caps (one on air injection, one below intake)
Verified Vacuum bypass (under intake) not leaking
Dipstick seal
Oil Filler Cap Seal
New Magnecor Wires
New Champion Plugs properly gapped
New Pertronix distributor
Pertronix 3ohm coil
New/Rebuilt fuel injectors and seals
Cleaned throttle body
Verified throttle body gap at .002
Cleaned/tested various grounds
Verified ignition timing
Set idle a touch high (900rpm). 700rpm in gear, 600rpm in gear with compressor on.
New Coolant Temp Switch
New O2 Sensor (3 wire)
Teflon tape on amplifier bolts
Ran Techron and more recently BG44K fuel system/intake cleaners
Ran both Premium (93RON) and Regular unleaded fuels (87RON)
Verified Compression in spec
Fresh 10W/40 Brad Penn synthetic blend oil for older cars
Verified charging system and battery up to snuff
AFM set to two turns out (idles/runs best here...actually idles best in open loop...O2 disconnected...just a little too rich)
AFM is original and doesn't appear to ever have been opened.

Next up:

Taking to shop to run on gas analyzer. Concerned however that they'll only make it leaner (which in my case seems crummier)
Replace AAV hoses (on backorder). I did already verify functionality of valve.
Replace throttle switch seal
Have valves checked/adjusted as needed

Last resort:

Swap ECU
Swap AFM

What do you guys/gals think? Am I missing anything (other than my sanity)?

Thanks in Advance,
Doug M

 

Doug, may I ask: If, as you say above, the car runs well through all rpm ranges but misses once in a while at idle, and this is a known characteristic with these engines, why are you concerned??

I've Never had a car (including my work truck and Nix) that didn't miss at idle once in a while, on different cylinders at different times, but ran Very Well at all other ranges. I always thought that was just how it was.

Is it a matter of "It's Not Perfect," or has it something to do with local emissions regulations? If it passes your emissions checks, why not just drive the wheels off and pretend you have a bit of a cam?

You know what you're doing, don't you? You're allowing this tiny "fault" to kill your joy and ruin the fun of owing/driving one of these Wonderful cars! If something was Really amiss someone on one of these sites you've visited would have raised an alarm. But that hasn't happened or you wouldn't be asking again.

Stop Worrying! Start Driving!
(';')

 

Boy, did you sum that up well! As you can gather, I'm a perfectionist, and in particular with cars. It's pretty maddening at times. It starts as a fun distraction/hobby. Get her a good tuneup, detail and enjoy. Then it's the joy of tinkering...let's do a few small recommendations in the forums to smooth out this idle. Then, it's well we went this far, let's finish the job. Then, I'm not accepting failure. Then obsession...and finally acceptance or sell the car (not there yet!).

I beginning to think you are right.

From a practical side, I do like to drive the car daily but unfortunately sit for long periods in traffic. The idle wobble just gets annoying, or moreover, adds to me already being annoyed in traffic.

 

I have to agree with LnrB, you're chasing shadows by aiming for a perfectly smooth idle on the XK engine. The slightly lumpy idle is part of the car's character, they all do it! Sometimes obsession has to give way to acceptance - the animal is what it is.

If you seriously can't live with it, sell her on and buy an X300 with the AJ16 engine, that's a real smooth talker (not as much fun though!)

 

Funny thing, I've owned both an X300 and X350 variant. Loved the X300, but lacked the quirky charm of the XJ6. I wanted to love the X350, but no matter how I tried, I knew it was a Ford...and it didn't have that Jag smell that I lusted after.

Both your posts have been helpful in evaluating the "old girl". I will finish up the last of my list, but I'll do so out of good maintenance rather than idle improvement.

Who knows, maybe someday AJ6 Engineering will come up with a "Smooth Idle Module" for $39.95! Hell if science can invent Propecia to regrow hair, anything is possible!!

 

Have you performed a leak down test, it seems you have done your research on all the common issues with these cars.

Possibly a gummed up inlet/exhaust valve might not be letting it seal properly sometimes, once in the revs you wouldn't notice it.

Maybe run a seafoam/subaru upper engine cleaner or similar through the intake system to eliminate the possibility.

Is all your emmision equipment operating properly? EGR valve, air injection setup etc

 

I tried the Subaru cleaner and every other suggestion thrown my way, made no difference in my case. After months of chasing the lumpy idle I have lived with it for 18 months and take it as part of the charm.

I recently fitted an electronic ignition from an S3, I think it made a slight difference. But that might just be wishful thinking, it's still a bit lumpy but not like it was 2 years ago.

Rebuilding the carby's improved it a lot, but still just a smoother lumpy idle if that makes sense.

 

arrrrrrrrhh, when I be a lad, a lumpy idle was a status symbol !

If its any consolation my Toyota Hi-Lux started rough idling at about 10,000 kms and is still doing it 400,000kms later. Some very smart people have had a look (not dealership) and havent been able to find anything without being able (allowed actually) to tear it down.

My answer, wind it up a 100rpm

 

+1 on that.

I won't tell how much it cost to get the lumpy idle on my bike, but ZZR cams,head job and rebuilding four carby's and re jetting with a stage 2 kit and pod filters, then having the power commander set on a dyno. $$$$ I should be spending on sensible things like painting the bathroom or fixing the gardens.

But it idles like a hot rotary and pulls like a school boy up high in the revs. And wheelie happy in the mid range. Goes pretty well for a 17 y/o motorcycle. Just wish I got out on track days more often.

sorry.

 

If not already done have the injectors flow tested. You might have one or two at the low (or high) end of the acceptable range.

The jiggly idle is a real bugaboo. I'm not aware of anyone who has really cured it.

Oddly, all of my Jags over the years have suffered some sort of idle quality problem X300, XJS, XJ6 Series 3. Annoying! Especially when I can jump into my 20 year old Honda or Ford work truck and feel a *perfect* idle!

Cheers
DD

 

Where I grew up it still is!!
Time moves slowly in the Great American Outback.
(';')

 

1. NIX is one good looking gal, whatever minor foibles she may have.


2. Each of my cars idle nicely. But, the Jaguar has a bit of a lope on start up. As it goes away rather quickly, it is of no concern to me.


3. If the car in question merely rolls a bit at idle and does not stall, it seems just fine.


4. A cure is possible. but not sans herculean effort. Possibly cam design.


5. I do not recall that the idle in my car as DOHC powered was an issue to me. It ran just fine. That is til Stockton!!


Carl

 

I think I was clouded by posts from "Tmack" on jaglovers who's successful elimination of lumpy idle was posted on Coventry West's website.

I often forget, that while forums are great, anecdotal evidence can be dangerous!

 

Ted Macklin; great guy. Yes, he really grabbed the rough idle problem by the horns...expended a LOT of effort... and made great strides. In the end, though, I don't think he was ever 100% satisfied with the results. But I might be mis-remembering. His story is an excellent example of a 'stack up' of minor faults all contributed to a single symptom


cheers
DD

 

Yup, Ted is a perfectionist. Lofty goals, and the dedication to achieve them, no question.


Conclusion is that each of us has a level of tolerance for flaws,
all different !!


Viva la difference !!!


Carl

 

So, in summary, what I'm hearing is keep your car in tune, get rid of major air leaks, drive it and stop whining! I can live with that.

Thanks to all for sharing. Frankly, until this post, I had no idea how truly common this issue (correction: quirk) was.

I'd certainly love to hear anyone else's experience as well.

 

Referencing status symbols once again, remember that the original XK was bred as a racing engine i.e. in its element when wound up, not so much when idling around. The essential DNA goes right through all XK engines which is evidenced by the cat's impatience when asked to hold unnaturally steady at the lights. How cool is that for pure status!

 

Wart (2001 Ford Windstar) also has a *Perfect* idle, but has about as much personality as a wet dishrag.

And, Doug, of your fleet, which would you rather drive? The *perfect* idle, or The Jaaag?
(';')

 

Racing engine? Yeah, sorta early on. But, then, it veered away. The DOHC and hemi combustion chamber breathes exceptionaly well.
Great for higher RPMs.


But, the stroke grew!!! More litres, more power. OK, sorta.
Long stroke engines create the best torque at lower RPM's. Not o mention wild piston speed when revved tight.


Why not a bigger bore to get those litres? over square or equal bore and stroke engines produce RPM's and power!!!


1. In the UK, tax is based on the bore!!


2. The block casting is limited as t a larger bore.


3. Sir Lyons funds had a limit.


4. Sir Lyons wanted an engine that was different and looked good. That he got.


Would an OHV engine in 4.0 or so produce race type HP. Oh, yes,
AMC's version in a truck set records on the salt flats!!!


My Jeep has a version of those engines!!!


Carl

 

Can't dispute any of that Carl, except, "sorta". In the day of course, they were nothing short of legendary!

The XK may have evolved along the way, but it's history and proven pedigree are undeniable. A little licence taken? Works for me!