1988 xjs h&e
#1
1988 xjs h&e
I recently purchased a 1988 XJS with the V-12. The car appears to run fine but the idle is to high. 1,100 to 1,200. I believe is should be around 600-700. I notice a mechanical adjustment at the side and rear of each cylinder bank but I'd rather not make adjustments until I know for sure what I'm doing.
Any help appreciated.
Ken
Any help appreciated.
Ken
#2
#3
I recently purchased a 1988 XJS with the V-12. The car appears to run fine but the idle is to high. 1,100 to 1,200. I believe is should be around 600-700. I notice a mechanical adjustment at the side and rear of each cylinder bank but I'd rather not make adjustments until I know for sure what I'm doing.
Any help appreciated.
Ken
Any help appreciated.
Ken
The idle speed on the V12 is adjusted and controlled by an Auxiliary Air Valve (sometimes called the Extra Air Valve). Do not touch the throttle linkage to adjust the idle until you know the AAV is working correctly. The AAV is situated just to the rear of the B bank inlet manifold, just after it, and is bolted to the head, with short right-angled 1 inch diameter rubber pipe leading to the end of the manifold. It is item 6 in this diagram:
On the inlet piece of the AAV (near what is labelled as 10) you will see a large nut. This is the idle speed adjuster, believe it or not! Screw it in, once the engine is warmed up, to slow the idle.
BUT, it is almost certain that yours is jammed, as they all do jam. It is not the adjusting screw that jams, but the mechanical part of the valve which is meant to gradually close off the air source as the engine warms up. New ones are available, and it is possible to rebuild them yourself, post for help on that.
#4
Hi Ken
Here is a Photo of the AAV to go with 'Gregs' diagram
The AAV Auxiliary Air Valve on a V12 XJS showing the Adjusting Screw
If the Car hasn't been used for a while, then as 'Greg' said they gum up but the good news is that once you have done a few journeys, they can also free themselves off and start working again
Here is a Photo of the AAV to go with 'Gregs' diagram
The AAV Auxiliary Air Valve on a V12 XJS showing the Adjusting Screw
If the Car hasn't been used for a while, then as 'Greg' said they gum up but the good news is that once you have done a few journeys, they can also free themselves off and start working again
Last edited by orangeblossom; 05-12-2018 at 03:42 PM.
#5
Idle adjustment
Welcome to the elite Ken.
The idle speed on the V12 is adjusted and controlled by an Auxiliary Air Valve (sometimes called the Extra Air Valve). Do not touch the throttle linkage to adjust the idle until you know the AAV is working correctly. The AAV is situated just to the rear of the B bank inlet manifold, just after it, and is bolted to the head, with short right-angled 1 inch diameter rubber pipe leading to the end of the manifold. It is item 6 in this diagram:
On the inlet piece of the AAV (near what is labelled as 10) you will see a large nut. This is the idle speed adjuster, believe it or not! Screw it in, once the engine is warmed up, to slow the idle.
BUT, it is almost certain that yours is jammed, as they all do jam. It is not the adjusting screw that jams, but the mechanical part of the valve which is meant to gradually close off the air source as the engine warms up. New ones are available, and it is possible to rebuild them yourself, post for help on that.
The idle speed on the V12 is adjusted and controlled by an Auxiliary Air Valve (sometimes called the Extra Air Valve). Do not touch the throttle linkage to adjust the idle until you know the AAV is working correctly. The AAV is situated just to the rear of the B bank inlet manifold, just after it, and is bolted to the head, with short right-angled 1 inch diameter rubber pipe leading to the end of the manifold. It is item 6 in this diagram:
On the inlet piece of the AAV (near what is labelled as 10) you will see a large nut. This is the idle speed adjuster, believe it or not! Screw it in, once the engine is warmed up, to slow the idle.
BUT, it is almost certain that yours is jammed, as they all do jam. It is not the adjusting screw that jams, but the mechanical part of the valve which is meant to gradually close off the air source as the engine warms up. New ones are available, and it is possible to rebuild them yourself, post for help on that.
I found the adjustment screw. I just applied some WD-40 to the threads. I'll warm up the engine tomorrow and attempt to adjust. How much would I expect to turn to notice a change in the RPM? 1/8-1/4-1/2?
If the screw will not turn in would you suggest turning it out then back in? The car has been driven on 4 occasions about 50 miles since coming out of Winter storage. What is the target RPM for idle?
Regards Ken
#6
#7
Turn the adjuster screw all the way in. target idle is about 700 rpm in neutral, engine fully warmed up. If the screw will not go in, undo it and try again. IF it is all the way in and the idle does not change, then the unit is jammed open (very usual). You can try to rebuild it or buy a new one.
See post 9 in this thread for Grant Francis' rebuild document.
https://www.jaguarforums.com/forum/x...ebuild-119510/
Last edited by Greg in France; 05-14-2018 at 04:17 AM.
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#8
Idle adjustment
Correct.
Turn the adjuster screw all the way in. target idle is about 700 rpm in neutral, engine fully warmed up. If the screw will not go in, undo it and try again. IF it is all the way in and the idle does not change, then the unit is jammed open (very usual). You can try to rebuild it or buy a new one.
See post 9 in this thread for Grant Francis' rebuild document.
https://www.jaguarforums.com/forum/x...ebuild-119510/
Turn the adjuster screw all the way in. target idle is about 700 rpm in neutral, engine fully warmed up. If the screw will not go in, undo it and try again. IF it is all the way in and the idle does not change, then the unit is jammed open (very usual). You can try to rebuild it or buy a new one.
See post 9 in this thread for Grant Francis' rebuild document.
https://www.jaguarforums.com/forum/x...ebuild-119510/
I have good news. After turning the bolt in one ratchet click at a time (total turn about one) I was able to drop the RPM from about 1,200 down to about 800.. I decided to leave it there for now till I drive the car more. Total mileage on the car is 72,300, but only about 75 after a 6 month storage. After a couple hundred miles I will try to drop the idle to 700 as you suggested. I was prepared to purchase a new Aux-air valve but it looks as if a have a reprieve. I'll keep you posted if anything changes. Thank you again for all your help.
Regards
Ken
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