Currently trying to get my idle down on my 1983 xjs.read kirbys e book aav worked good upon testing .had vehicle at norm temperature and plugged hole where it goes to air filter housing not much difference. Did the checks for vacum leak with carb cleaner around intake gaskets ,hoses etc nothing.currently checking overun valves did notice left side was sucking quite a bit at normal temp plugged with finger .so going to tighten down spring per kirbys book on both sides so they stay closed. I took off the vacum line to the ecu good vacum and started to run really rich . Idle did drop is that what should happen? Also checking vacuum lines under right hand manifold .Does any of those two way and three way valves ever go bad? Timing is spot on . Could use some words of wisdom please.
Richard,
I have some words of wisdom, “check and/or adjust the throttle butterflies”.
The butterflies should be set to 0.002 inches, the procedure is in the XJ-S Repair Operation Manual. You must make sure that the throttle linkage bushings (Part number C34388) are present and not cracked or missing like mine were otherwise the adjustment is a waste of time. The attached pictures show that bushing on the end of the throttle coupling shaft. I tried some aftermarket bushing but they were too hard for me to put into the hole in the mount plate on the end of the shaft even after I softened them with a heat gun. I purchased the OEM bushings from the local dealership and they were easy to install and clearly made of a superior material for this application. BTW others on this list have replaced these bushing with ones that they machined from nylon, brass or other materials. Since I don’t have those tools or skills I purchased the OEM bushing and they have worked fine for me for several years.
0.002 is a very narrow opening, it’s almost closed. Once I got them close I turned the adjusting screw one flat at a time to find the sweet spot between the two butterflies and the AAV that gave me the idle I wanted warm and the start up idle.
BTW, if you do need these bushings purchase a spare or two. They are a bit challenging to install and if you drop one inside that V12 engine bay you will never find it again. There is no need to ask me how I know that. 
Regards,
Paul M. Novak
1990 Series III V12 Vanden Plas
1990 XJ-S Classic Collection convertible
1987 XJ6 Vanden Plas
1984 XJ6 Vanden Plas
1969 E-Type FHC
1957 MK VIII Saloon
Ramona, CA USA
Thank you Mr. Paul Novak. Spent the day adjusting butterfly clearance and throttle rod adjustments and throttle stop adjustments. This car has never idled this good. And not running so rich either used to smell the fumes of a somewhat rich running mixture Greatly appreciate your wisdom. .
Richard,
I am glad that I was able to help. Looks like we both got lucky this time.
I own, drive, and do most of the servicing and repairs on our two six Jaguars. I got the 1990 XJ-S convertible (5.3L V12 with Marelli ignition) for my wife in 2005 and have tackled many projects on it as restore that car to is original beauty after our 12 years and 60K+ miles. With the repaint, new convertible top that I installed, the refurbished trunk, and recent engine bay work, I have performed many of the servicing and repairs that normally get discussed here on this list. I got my 1990 V12 Vanden Plas (5.3L V12 with Lucas ignition) in 2011 and although that car was in exceptionally good shape after a restoration in 2003, stuff happens. I try to help out others when I can, and I am glad that my advice helped you out. There are many others on this list with more knowledge and experience that I have, and I learn things regularly on the Jag-Lovers lists that I am on that help keep my Jaguars running, and my restoration projects going forward.
These cars are great for those who are willing to tackle the work themselves. If I had to turn to someone else to do the work I would have given up this hobby many years ago.
Regards,
Paul M. Novak
1990 Series III V12 Vanden Plas
1990 XJ-S Classic Collection convertible
1987 XJ6 Vanden Plas
1984 XJ6 Vanden Plas
1969 E-Type FHC
1957 MK VIII Saloon
Ramona, CA USA
Totally agree went to college for automotive technology I learned a bulk from my father.Born in Jamaica grew up in England.He was a city and gill mechanic always talked about working on Sterling Moss race car.Drove double decker buses.Rip pops.
Paul:
Kudo’s on the blue shop paper under the work to catch any drops!!!
Ain’t it much better to work on clean stuff.
Carl
Richard.
Great to see that fixed. I note however in your check list of potential problems you didn’t mention the PCV valve. This should restrict air flow at idle and open while at higher revs. My 82 had the PCV fail causing very high revving. The high hiss gave it away. Cheap fix.
Trev