Fuel System - Poor Driveability/Idle Quality
19-36DATE
10/95
MODEL
XJ12 Sedan 1994 MY
XJ12 Series III
XJS V12
Poor Driveablity - Check Throttle Synchronization
This Bulletin applies to the following vehicles:
All 1994 MY XJ12 Sedan (VIN 673299-708757)
All Series III XJ12 Sedan (up to VIN 487641, 1979-92 MY Canada, 1979 MY USA)
All Jaguar XJS V12
ISSUE:
Poor throttle valve synchronization may cause customer complaints of poor driveablity and idle quality.
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.
An additional revision was made to the method for setting the throttle linkage to improve synchronized opening of both throttle valves starting with:
ENGINE NO. VIN
8D12554 222252
ACTION:
When diagnosing driveability or idle complaints, check the throttle valve and linkage settings as described in the following procedure before any further diagnosis or repair.
Perform a road test after adjusting the throttle valves and linkage. If the complaint still exists, refer to the diagnostic procedures in the Vehicle Service Manual.
SETTING THROTTLE VALVES
NOTE:
The factory throttle stop setting should not be disturbed unless a noticeable fault is present.
1. Check that both throttle valves are centered horizontally and vertically in the throttle bodies.
2. With the throttle valve closed, use a feeler gauge to check the clearance between the throttle valve and the throttle body (Illustration 1).
Throttle valve checking clearance: 0.001 - 0.003 inch (0.025 - 0.076 mm) Check the clearance at the bottom as well as at the top of the throttle valve. If a significant difference is found between the top and bottom measurements, the throttle valve may be offset on its shaft. If both measurements are within the above range, do NOT adjust the throttle stop screw (Illustration 1).
3. If adjustment is necessary, set the throttle stop screw to achieve the following throttle valve clearance range:
Throttle valve setting clearance: 0.001 - 0.0015 inch (0.025 - 0.040 mm). After completing throttle valve adjustment, seal the locknuts with a dab of paint.
4. Repeat the checking procedure on the opposite throttle valve.
SETTING THROTTLE LINKAGE
NOTE:
Starting with XJS VIN 222252 (1995 MY), the linkage has been set at the factory using special equipment to obtain simultaneous opening of both throttle valves. Do not change these settings unnecessarily.
Use the following procedure to obtain the required backlash in the throttle linkage to ensure correct synchronization of throttle opening.
1. Loosen both locknuts on the two linkage rods between the center throttle turntable and the throttle levers.
2. Disconnect one linkage rod from its ball pin on the linkage rod bracket.
3. Position a 0.079 inch (2.00 mm) spacer between the linkage rod bracket and its stop (Illustration 2).
4. Turn the linkage rod that is still connected to increase its length until the throttle lever clears its stop screw.
5. Shorten the linkage rod until the throttle lever just touches its stop screw. Tighten both lock nuts on the linkage rod.
6. Connect the second linkage rod and repeat steps 4 and 5 to adjust its length.
7. Remove the spacer inserted between the linkage rod bracket and its stop.
8. Check the backlash by turning the linkage rod bracket of the throttle turntable slightly clockwise. A gap should appear between the bracket and its stop before either throttle lever leaves its stop screw. Gap dimension: 0.062 - 0.094 inch (1.57 - 2.39 mm)
9. Both throttle levers should leave their stops at the same time. Satisfactory synchronization is possible if the second throttle lever moves from its stop after the first throttle lever within a maximum additional increase of 0.030 inch (0.76 mm) in the gap.
10. Release the linkage rod bracket to allow the turntable to return to the closed throttle position. Check that the linkage rod bracket is now in contact with its stop. If any gap is present, repeat steps 1 through 10.
Perform a road test after adjusting the throttle valves and linkage. If the complaint still exists, refer to the diagnostic procedures in the Vehicle Service Manual.
WARRANTY INFORMATION: