Checking the operation, removing and installing the air flow meter (BMW 5 Series E28)

Examination (l-Jetronic systems)

1. Disconnect the air flow meter from the inlet fitting. Carefully open and close the sensor flap and check for binding. The flap can bend during backfires, causing incorrect resistance measurements. The flap can bend and remain in a partially open position, causing rich mixture and stalling at idle.

2. Disconnect the electrical connector from the air flow meter.



3. Check the resistance between contacts 7 and 8 with an ohmmeter. The resistance should increase steadily (without "flat spots") as the sensor flap is slowly moved 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 that the resistance between contacts 8 and 9 is correct (see the 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 On-board electrical equipment system). Connect the flow meter connector. Make sure the ignition is off. Disconnect the connector from the ECU (located under the dashboard on the right) and check the resistance between pins 7 and 8 with an ohmmeter. Carefully remove the cover 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 there are any differences in the results, there may be breaks or short circuits in the cable.

Functional check (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 the resistance between the marked pins of the ECU electrical connector with an ohmmeter and check the resistance change when moving the paddle. On early Motronic systems use pins 7 and 9.



3. On later models - contacts 7 and 12.

4. The resistance should increase continuously (without "flat spots") as the sensor petal moves from the fully closed position to the fully open position.

Early Motronic systems feature a 35-pin electrical connector; later Motronic systems used 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 the air cleaner).





3. Loosen the nuts and remove the flow meter from the engine compartment or from the air cleaner.



4. Installation is the reverse of removal.