Examination (L-Jetronic systems)
1. Disconnect the air flow meter from the inlet fitting. Carefully open and close the sensor shutter and check for binding. The shutter can be bent during backfires and thus lead to incorrect resistance measurements. The choke may buckle and remain in a partially open position, causing the mixture to become rich and the engine to stall at idle.
2. Disconnect the electrical connector from the air flow meter.
3. Check the resistance between pins 7 and 8 with an ohmmeter. The resistance should increase continuously (without "flat areas") by slowly moving the sensor damper from the fully closed position to the fully open position.
4. Also check the intake air temperature sensor (inside the flow meter). Check with an ohmmeter for correct resistance between pins 8 and 9 (see illustration above). The resistance at 20°C should be between 2200 and 2700 ohms.
5. If the resistance values are correct, check the cables (see chapter Onboard electrical system). Connect the connector to the flow meter. Make sure the ignition is off. Disconnect connector from ECU (located under the dashboard on the right) and check the resistance between pins 7 and 8 with an ohmmeter. Carefully remove the cap from the flow meter and observe the change in resistance as it moves from the closed position to the fully open position. The test result should be the same as the previous test. If any differences are observed in the results, then there may be breaks or short circuits in the cable.
Function test (Motronic systems)
1. Make sure the ignition is off. Remove the ECU Access Cover (see chapter Engine management and emission control systems) and disconnect the cable connector.
2. Check with an ohmmeter the resistance between the marked pins of the ECU electrical connector and check the change in resistance as the tab is moved. On early Motronic systems, use pins 7 and 9.
3. On later models - pins 7 and 12.
4. Resistance must continuously increase (without "flat areas") when moving the sensor blade from the fully closed position to the fully open position.
Early Motronic systems are distinguished by a 35-pin electrical connector; late Motronic systems use a 55-pin connector.
5. If the resistance value is incorrect, check the cable.
Removal and installation (all systems)
1. Disconnect the electrical connector from the flow meter.
2. Remove the air cleaner (see Section Removal and installation of the air cleaner).
3. Turn away nuts and take the flow meter from an impellent compartment or from an air cleaner.
4. Installation is reverse to removal.