M/T

Hunting (Repeated Acceleration and Deceleration) 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

Required Special Tool:
- MB991223: Harness Set

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)

Q: Is the voltage within specifications?

YES: Go to Step 2.

NO: Replace the vehicle speed sensor. Refer to Combination Meter Assembly and 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:
a. Connect the positive battery terminal to auto-cruise vacuum pump connector terminal 1 and the negative battery terminal to terminals 2, 3 and 4. Then the vacuum gauge should read 27 kPa (8.0 in.Hg) or more.
b. 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.
c. 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.

Q: Are all of the above values satisfied?

YES: Go to Step 3.

NO: Replace the auto-cruise vacuum pump. Then 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.

Q: Is the vacuum actuator damaged?

YES: Replace the vacuum actuator. Refer to Throttle Body Assembly. Then check that the malfunction is eliminated.

NO: Check that the malfunction is eliminated. If the malfunction is eliminated, replace the auto-cruise control-ECU. Then check that the malfunction is eliminated.