7. Hunting Occurs At the Set Vehicle Speed

TECHNICAL DESCRIPTION (COMMENT)
The cause is probably the malfunction of the vehicle speed sensor or incorrect vacuum in the auto-cruise control vacuum pump or actuator.

TROUBLESHOOTING HINTS
- Malfunction of the vehicle speed sensor.
- Malfunction of the auto-cruise control vacuum pump.
- Malfunction of the actuator.
- Malfunction of the auto-cruise control-ECU.

DIAGNOSIS




STEP 1. Check the vehicle speed sensor.
1. Remove the vehicle speed sensor and connect a 3 - 10 kohms resistor as shown in the illustration.
2. Turn the shaft of the vehicle speed sensor and check that there is voltage between terminals 2 - 3. (one turn = four pulses)
If there is a voltage between terminals 2 - 3, go to Step 2.

If there is no voltage, replace the vehicle speed sensor. Then check that the malfunction is eliminated.




STEP 2. Check the auto-cruise vacuum pump.
1. Disconnect the vacuum hose from the auto-cruise vacuum pump and connect a vacuum gauge to the vacuum pump.
2. Disconnect the vacuum pump connector.
3. Check the auto-cruise vacuum pump and valves according to the following procedure:
1. Connect the positive battery terminal to auto-cruise vacuum pump connector terminal 1 and the negative battery terminal to terminals 2, 3, and 4. The vacuum gauge should read 27 kPa (8.0 in Hg) or more.
2. The vacuum should be maintained when terminal 4 is disconnected from the negative battery terminal while terminals 1, 2, and 3 remain connected. Then the vacuum gauge should read 0 kPa (0 in Hg) when terminal 2 is disconnected from the negative battery terminal while terminals 1, and 3 remain connected.

3. The vacuum should be maintained when terminal 4 is disconnected from the negative battery terminal while terminals 1, 2, and 3 remain connected. Then the vacuum gauge should read 0 kPa (0 in Hg) when terminal 3 is disconnected from the negative battery terminal while terminals 1, and 2 remain connected.

If all of the above values are satisfied, go to Step 3.

If any of the above values are not satisfied, replace the auto-cruise vacuum pump. Then, confirm that the malfunction is eliminated.




STEP 3. Check the vacuum actuator.
1. Disconnect the vacuum hose from the vacuum actuator, and then connect a hand vacuum pump to the vacuum actuator.
2. Apply a vacuum and check that the throttle lever moves and the vacuum is maintained.

If faulty, replace it. Check that the malfunction is eliminated. If faulty, replace vacuum actuator. Check that the malfunction is eliminated.