Automatic Transaxle
Hunting (Repeated Acceleration and Deceleration) Occurs at the Set Vehicle SpeedTECHNICAL DESCRIPTION (COMMENT)
The cause is probably the malfunction of the output shaft speed sensor or PCM or incorrect vacuum in the auto-cruise control vacuum pump or actuator.
TROUBLESHOOTING HINTS
- Malfunction of the output shaft speed sensor.
- Malfunction of the PCM.
- Malfunction of the auto-cruise control vacuum pump.
- Malfunction of the actuator.
- Malfunction of the auto-cruise control-ECU.
DIAGNOSIS
Required Special Tool:
- MB991502: Scan Tool (MUT-II)
- MB991223: Harness Set
STEP 1. Check the vehicle speed signal.
CAUTION: To prevent damage to scan tool MB991502, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991502.
1. Using scan tool MB991502.
2. Connect scan tool MB991502 to the data link connector.
3. Turn the ignition switch to the "ON" position.
4. Read the MFI-DTC.
5. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the MFI-DTC P0720 is output?
YES: Refer to Diagnosis - Diagnostic Trouble Code Chart.
NO: Go to Step 2.
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:
- 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.
- 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.
- 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.