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Circuit Test D - Speed Fluctuates

  1. Verify condition. Check throttle linkage for proper operation and adjustment. Service and adjust as necessary. On Continental, Mustang, Sable, Taurus, Tempo and Topaz, if throttle linkage is okay, check continuity on circuits No. 147, 148 and 149 between servo and amplifier. On Escort and Tracer, check for continuity on all circuits between servo and amplifier. On all models, if continuity is not present, repair open circuits. If continuity is present, go to next step.
  2. On Continental, Cougar, Sable, Taurus and Thunderbird, check vacuum hoses. Repair and replace as necessary. If vacuum hoses are okay, test check valve. On Cougar and Thunderbird 3.8L SC, also check aspirator check valve. Apply 18 in. Hg vacuum to both check valves. If vacuum does not hold, replace check valves. If check valves are okay, on all models except Cougar and Thunderbird, perform appropriate SERVO ASSEMBLY  test under COMPONENT TESTS.
  3. If servo does not test okay, replace servo. On Continental, if servo tests okay, go to step No. 4). On all other models, if servo tests okay, check speedometer cables for proper routing, or crimping and binding. Service as required. If speedometer cables are okay, go to next step.
  4. Check VSS for free operation. If VSS is not operating freely, replace it. If VSS operates freely, perform VEHICLE SPEED SENSOR (VSS) test under COMPONENT TESTS  . Replace VSS as necessary. If VSS tests okay, test vacuum dump valve. Replace or adjust as necessary. If dump valve is okay, go to next step.
  5. Perform AMPLIFIER TEST  under TESTING. If cruise control problem is corrected after test, replace amplifier. If problem is not corrected, check circuit connectors for security.
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