Is there a simple “diy” solution(s) to adjust my idle speed? Currently running at 1200 - I can follow directions well, just not a mechanic. Any help would be appreciated!
Sdmarm,
Well, adjusting the idle in a 5.3L V12 can be a DIY job. We own and drive 2 5.3L V12 Jaguars (1990 XJ12, 1990 XJ-S convertible) and I have adjusted the idle on both. But “simple”? Hmmm…
It would help if you had a copy Service Manual and the correct tools. But the adjustments to make are first to check that both throttle butterflies are set to 0.002 in. using a feeler gauge and small wrench, and then to adjust the bolt on the side of the Extra Air Valve (EAV) with a wrench to raise or lower the idle to spec. This assumes that the engine timing is correct and that there are no vacuum leaks. Two common causes of high idle that can not be adjusted to spec this way are vacuum leaks (failed hoses and gaskets) and a frozen piston inside the EAV.
The EAV has an opening that allows more air (hence more fuel) into the engine when it is cold, but the opening is supposed to automatically close up as the engine heats up to reduce the amount of air (and fuel) to reduce the idle. The piston inside the EAV reacts to coolant temperature and can get stuck in the open (cold) position resulting in a high idle that can not be adjusted unless the EAV is removed, repaired, and/or replaced. Search the Jag-Lovers archives for “EAV” and “high idle” and you should find lots of helpful posts from others who have run across high idles and EAV problems especially in the V12 equipped XJ-S.
The EAV is located on the left rear side of the engine aft and beneath the intake manifold and close to the firewall.
BTW, if you haven’t already done so download Kirby Palm’s “Experience in a Book” from Jag-Lovers (it’s free) and read more about high idles and the EAV.
Paul
Good day Paul and thank you for your detailed reply. I did confirm appropriate “gap” and the attempted to adjust EAV. Moving bolt all the way in and then out, no variance in idle speed. I would now conclude a replacement is in order. However . . . . taking the car out to drive shortly after, the engine started to loose power and white smoke came pouring out of right tail pipe?!?!?! Yikes! Engine gauge did not register as over heating, oil pressure good. I let car sit for a short time then resumed trip to return home. Short distance, white smoke again from tail pipe, had car towed home. Any ideas? 1988 Daimler Double Six, 37000 miles V12 5.3
1 Like
PS . . . idle now fluctuates wildly
Sdmarm,
White smoke out if the right side tail pipe only is a classic symptom of a ruptured diaphragm in the transmission modulator. Your engine is now sucking transmission fluid into the right side intake manifold and burning it in the right side cylinders. Be careful that you don’t get low on transmission fluid before you fix it, otherwise this could get to be an expensive repair. I fixed this same problem in my wife’s 1990 XJ-S convertible (basically the same 5.3l V12 and GM400 transmission). I purchased an aftermarket modulator from a local autoparts store for about $25 USA. The OEM Jaguar part was also available at tge local dealership but much more expensive. You should also consider replacing the vacuum hose that goes from the modulator to the rear of the right side intake manifold while you are working in the area.
Paul
Sdmarm,
Yes, it sounds like your EAV piston is stuck in the open position. You should remove it and test it in a pot of hot water on the stove to verify that it has failed this way. Some people have had good luck freeing up the piston and getting it to operate properly again. Some info about this is in Kirby Palm’s book downloadable for free on Jag-Lovers. New EAV are hard to find and expensive. There are shops that rebuilt them. Once you confirm that the piston is stuck you will need to determine the best course of action for you to get a properly operating one installed.
Paul
Understood . . . approx. location of “modulator”
sdmarm,
The Vacuum Modulator, Jaguar part number EAC1726, is located on the right side of the transmission adjacent to the right side intermediate exhaust pipe. Access is from below. There is very little room to access the Vacuum Modulator to remove and replace it. It can be done without removing the exhaust pipes, but it wasn’t easy for me to do so because there is very little room to do so.
My copy of the Series III XJ12/DD6 Parts Catalogue (RTC9886CE of May 1985) has a nice depiction of the Vacuum Modulator on page 1E05L along with associated hoses and connectors. If you don’t already own a copy of this Parts Catalogue I can highly recommend it. Having the correct Jaguar Parts Catalogues for my six Jaguars took a lot of the mystery out of parts matters for me, but not all of them. 
Paul
Again . . . many thanks! Was able to find illustration in my XJS repair manual. That install is above my pay grade, lol. Have local transmission shop I will call on in the AM. Ordered both parts from SNG
When I removed and replaced the vacuum modulator I tested both the old one and new replacement one on my work bench side by side. The one I removed would not hold vacuum when tested with my Mity-Vac vacuum tester but the new replacement one held vacuum fine. This was the kind of positive confirmation that I like to see. After installing the new one I test drove the car, the white smoke from the right tail pipe was gone and the transmission shifted properly again. Again confirming that I properly diagnosed the problem and fixed it.
Because the transmission fluid got sucked up into the right side intake manifold I had transmission fluid leaking down on the right side of the engine for a while. It was also in the right air filter housing soaking the air filter which I also removed and replaced.
Good luck.
Paul
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In principle, a failed modulator may influence gear shifting, sdmarm - as Paul mentioned…
One crude test of modulator membrane failure is to disconnect modulator’s vacuum hose - and watch smoke disappear, as a confirmation. Point here is that the ‘smoke’ may be coolant through a bust head gasket. Which can be revealed by a compression test - or gradual loss of coolant. Just as a back-up plan…
Replacing parts without any investigations is throwing money at a problem - however, if it fixes the problem; it is money well spent…
Frank
xj6 85 Sov Europe (UK/NZ)
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“Right side”, “left side” is incorrect terminology and ONLY helpful to those same people who use the same incorrect terminology. “A” bank or “B” bank is correct and useful. I THINK your response would help me with the same issue as the questioner, but I have NO idea which is the “left” or “right” side. Is it while sitting in the car or while looking at the car??? Please be of some actual help by revising this response. Thanks
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I readily identify the right and the left side of a car, Bert - and everything inside relates to that…
And the ‘A’ bank is on the ‘right’ - identifying it by other means is a bit tedious…
Frank
xj6 85 Sov Europe (UK/NZ)
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Thank you very much for the kind response. After re-reading my question to you I realize I was rather harsh toward you and I do apologize for that. I do have another question for you regarding the high idle and AAV. Can I email you later about it?
Thanks again for the kind response. Sincerely, Bert Nelson