[xj-s] Throttle Linkage Adjustment

For anyone who wants to give this a go, here is the excerpt for the throttle
linkage adjustment:-

THROTTLE LINKAGE ADJUSTMENT: If the butterfly stop screws have been
disturbed, the linkage bushings have been replaced, or any other tinkering
has been done that could mess up the linkage adjustment, it should be
readjusted. Also note that several owners have found that a rough idle
cleared up when this procedure was undertaken, even though one wouldn’t�t
expect it to make any difference; the crossover pipe should deal with any
imbalance between sides.
I will endeavor to explain the process here more clearly.
In further developments, the mid-90�s cars with OBD II required much more
careful adjustment to avoid fault warnings. TSB #19-36, dated 10/95, says:
�Diagnostic Trouble Codes (DTCs) may be set if both throttle valves are not
synchronized to begin opening at the same time. The Manifold Absolute
Pressure (MAP) sensors will detect a difference in pressure between the two
intake manifolds, which leads to the setting of DTCs.
�The most common codes found are: P1106 P0106. The following DTCs may also
be set: P0107, P0108, P0125, P1107, P1128. Poor throttle valve
synchronization may also cause customer complaints of poor drivability and
idle quality.�
TSB #19-36 provides improved procedures for adjusting the throttle linkage
on the OBD II cars, but it can be applied to all V12�s with EFI. As a
result, these improvements have been incorporated into the following
descriptions of the adjustment procedures. Joe Bialy and Richard Mansell
provided some interpretations of this TSB. Mansell says, �I suspect there
are different TSB’s for the different models. I guess the contents are the
same but for a start the throttle pedestal is different on my '96 XJ12
compare to the XJ-S I owned so the picture with the TSB is different.�
The linkage requires five distinct adjustments, which must be done in order
because each affects the others. Before starting, disconnect the cross rods
from the throttle pulley by prying them off the ball joints, and remove the
air filter covers and elements. Loosen the locknuts and turn in the
butterfly stop screws until they don�t interfere with the butterfly motion.
It is highly recommended that you clean the throats before proceeding, using
some sort of solvent (see �Throttle Sticking� below) to get the areas where
the edges of the butterflies contact the housings nice and clean. Rather
obviously, check the condition of such things as the linkage bushings (see
above) before doing the adjustment.
Step 1: Loosen the screws holding each butterfly disk in its shaft, gently
press the butterfly closed so that it makes secure contact all the way
around, then retighten the screws. This centers the disk in the opening.
Step 2: Set the butterfly stop screws. This screw prevents the butterfly
from quite fully closing; if it closed completely, it could easily jam,
especially with temperature changes such as shutting off a hot engine and
then trying to start it the following morning.
To adjust the stop screw, open a butterfly, insert a 0.002� feeler gauge
between the butterfly and the housing, and let the butterfly close on it.
The earliest Jaguar repair procedures specified a 0.004� (0.105 mm) gauge,
but after 1978 it was changed to a 0.002� (0.05 mm) gauge – which works
fine for the earlier cars. Several have suggested a piece of paper works
better, since the metal gauge may be too wide or too stiff to work properly
against the curved side of the bore; use a micrometer to select a piece of
paper the correct thickness.
Whatever, with gauge in place, adjust the stop screw until it just touches
and tighten the locknut. Note, however, that this is much easier said than
done; you can turn the stop screw so easily that you can open the butterfly
right up and never know when you went from the screw not even touching the
lever to pushing the butterfly open. Roger Bywater suggests you do your
feeling with the feeler gauge rather than at the screw. Insert the feeler
gauge at the bottom, push the butterfly firmly closed on it, and give the
feeler a little tug so the butterfly grips on it. While pulling gently on
the feeler, turn the stop screw just until the butterfly starts to let go of
it. Try it a couple of times until you get the feel of the process, at
least well enough that you can do both sides the same way.
From the TSB: �An improved factory procedure for setting the throttle stop
screws, using an air flow measuring gauge, was introduced during the 1994 MY
production of V12 engines. All 1995 MY V12 engines are set at the factory
using this method.�
Step 3: Loosen the clamp on the lever at the rear end of the butterfly
shaft, directly below the cross rod attachment. Allow the spring to hold
the butterfly against the stop, and hold the cross rod attachment ball joint
in the idle position, where it contacts its own stop. Take up all slop in
the butterfly shaft coupling (adjacent to the butterfly stop) in the opening
direction, and retighten the clamp. Repeat for other side.
Step 4: Position a spacer 2mm (0.079�) thick between the bell crank and
its idle stop. Loosen the locknuts on the cross rods and adjust each link
such that the butterfly closes against its stop with that spacer in place.
Remove the spacer.
Step 5: Loosen the locknut on the full throttle stop screw on the throttle
pulley, and back the stop screw away. Hold the pulley in full throttle
position, noting that the butterflies are both full open. Adjust the stop
screw until it just touches the pulley and retighten the locknut. This stop
screw merely prevents stress on the linkage while the engine is at full
throttle and the kick down switch is in operation, and is not meant to
restrict full throttle.
Check for backlash at the turntable stop to be between 0.062-0.094�
(1.57-2.39mm) as it is rotated clockwise. Check that both throttle plates
leave their stops at the same time, but if they don�t, the TSB allows an
additional 0.030� of turntable travel to get the second throttle to move off
its stop.
Ensure that the throttle moves freely through the full range of motion.
Finally, check for no gap at the turntable stop with the throttle in the
closed position. Note that if the cruise control cable is too tight, it can
restrict the throttle linkage moving fully to idle.
You will need to warm up the car and readjust the idle speed, since the
butterfly stop screw positions have been altered.____________________________
Graham Murray '84 XJS H.E.
Jaguar Car Club of Austin