Hi fellas,
I am still trying to diagnose and repair a cold start issue on my '98 XJ8 VDP. After start up the engine slows to a high idle of about 850 rpm and I get a light 'clack, clack, clack' sound and the idle sounds like I'm misfiring. I have found that a slight increase in RPMs 'clears' this issue and then the engine idles smoothly. As I press the accelerator down I hear a single 'click' and then the idle smoothes out. It's like something is freeing up or engaging and allowing proper aspiration.
This symptom has been going on for a year now and I originally thought I was getting timing chain noise and changed out the entire primary and secondary components. The timing is intact and the overall visual condition of the cams is excellent. I have also replaced all the plugs and checked over all harnesses, coils, vacuum lines and hoses for irregularities. The noise was there before, during and now after all my tinkering. The only code I have for OBDII is P1000 which I believe is a system check cycle not cleared since I last disconnected the battery. I do not get any MIL illumination.
I am now thinking it might be a hydraulic lifter/ valve train issue, or maybe low oil pressure from a bad pump, gummed pickup screen or faulty sender as the root cause. I had the car in to re-pack a wheel bearing the other day at a local garage and asked if they could manually check the oil pressure for me but to no avail. Before I start digging deeper (and making a great big mess) does anyone have any advice or familiarity with this symptom?
Yours humbly,

John W

IT sounds like you may need to put in on a diagnostics computer. Cars these days have so many sensors and relays and computers that it's not like the old days where you can easily diagnose the basic engine components. For example, my son's 2000 Saturn LS just had a problem where intermittently it would act like it was running on 5 cys (its a 6 cyl). I did all the usual stuff (plugs, checked timing, ran some injector cleaner through it, etc) but the problem persisted. I finally too it to Hogan's Automotive and they put it on their diagnosis computer and found that the problem was the computer on the LS sometimes causing one of the injectors to misfire. Solution: Replaced the computer with one from a salvage yard. Problem solved. Without a means of checking the codes, I'd have never been able to figure it out.

Hi Basil,
It could be a computer issue, I am not sure if the two issues are related but on rare occasion when I try to start my car the dash stays in the "system check" mode. This is simply corrected by trying again and it starts. I am also not sure who around me has the diagnostics computer that reads Jaguese computer language. Seems like it's time to visit the dreaded Jaguar dealer$hip!

John W

If it were my issue I'd go thru a couple oil changes adding Marvel Mystery Oil to the mix. A pint in place of the first half-quart and see if that doesn't free up the issue.

No guarantees, just an opinion.

Hi DrEntropy,
I haven't tried Marvel Mystery Oil yet but I did try a quart of Sea Foam for a week and then changed the oil to 10W30 for S and G's. Does Marvel Mystery Oil claim to do similar things as Sea Foam? Or have I made my situation worse?

John W

Certainly not worse, methinks.

Similar claims on MMO and Sea Foam. I never used Sea Foam but know plenty of folks who have, results vary. Same with MMO. It doesn't "magically" fix out-of-tolerance issues but it can free up some well craminated oil port issues.

Your description could be a sticking valve, too. Before a tear-down I'd give another shot at a snake oil like MMO.

I took the cam covers off and rotated the crank to watch the lobes and shim movement with nothing that stood out. My timing is still good since I last monkeyed with it. I then tested the compression in all eight cylinders by cranking the starter with the fuel pump disconnected. All readings seemed pretty close to each other (159, 155, 160, 145, 158, 164, 159, 155). Would this merely rule out a valve being stuck open? or should I now be looking elsewhere(eg. pull the heads)? I will be using the MMO for a few oil changes to see if it helps before I do anything drastic. My oil pressure seems ok because oil was being pumped up to the cams when I was cranking for the comp test. Whatever this tapping noise is, it goes away immediately with just a slight press on the accelerator pedal.

Valve sticking in a guide when cold is my "best WAG", John.

The MMO is an excellent "upper cylinder lubricant" and ~if~ there's a bit-o-crud in a guide the stuff should help.

Hey, it couldn't HURT.

At this stage I will keep changing the oil with MMO but time is running out! I have a month a half before we move back to Australia. I ran the numbers for potentially taking her with me to Australia and doing a RHD conversion but the quotes I received for the conversion were astronomical. So drats, my beautiful cat must be sold. My biggest fear is that some 18 y/o kid will buy it and wrap it around a tree. I sold a VW Jetta a few years back and it was totalled within a week. The fellow wasn't hurt but he didn't have comprehensive insurance!

John, how much will you be asking for it? I can put the word out around here for you......

Hi Steve!
Thanks for your help,
I am asking $4750 on craigslist but I will drop that number significantly for a British Car enthusiast, and besides, you know all of my history with the car so far!!! If I don't sell her within 4 weeks than she will be dropped off at CarMax, with me weeping and nashing my teeth...

John W
(920) 428-1091

How many miles John? My dad has a '95, maybe he'll consider an upgrade?

Hi Steve,
My beautiful Jaguar has 137k on the clock. I can send you a link from Walgreens where I have 36 photos of the car, inside and out. I'll PM it to you as soon as I can!
John W