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Range Rover 3.5 Litre (non cat) Airflow Meter Tamper Checks

The wiper and flap tension mechanism are located under the rectangular plastic cover (approx 2.5 by 3.5 inches) on the top of the airflow meter. The airflow meter is a precision mechanical balance and is sealed for life at the factory - the plastic cover should never be removed. The mechanism should NEVER be adjusted or lubricated or cleaned - it is meant to look as if the wiper arms have scored the carbon tracks! Idle mixture adjustment is via sunken hex head screw in body of airflow meter.

If this cover is loose it has been removed. Do not mistake factory resin sealer beads for evidence that cover has been forced off - look for scratches and/or loose cover. If there is no evidence cover has been removed LEAVE IT ALONE and do not attempt spring adjustment - IT IS NOT WORTH THE PROBLEMS SPRING TENSION ADJUSTMENT WILL CAUSE!

Also - Please be aware that airflow meters from vehicles fitted with LPG gas may have suffered from blowback damage which may make any mixture adjustment ineffective. ALWAYS ask owners of LPG vehicles if they have had blowback problems. If the flap sticks or feels rough when moving by hand it is probably beyond repair and should be replaced.

If the airflow meter has been opened AND 'adjusted' in an attempt to overcome running problems caused by ECU failure, it MAY be necessary to re-adjust the spring tension after the ECU problems have been rectified. ALWAYS ROAD TEST WITH YOUR REBUILT ECU - there may be no need to re-adjust airflow meter! If car runs fine and CO is adjustable then airflow meter should be OK.

Re-adjustment Procedure

    1) Before commencing re-adjustment it is VITAL that ALL possible problems that could affect correct engine operation have been sorted. This includes head gasket failures, ignition advance/retard fully working, ECU rebuild and coolant temperature changed + full service carried out.
    2) If possible, compare flap tension with another airflow meter by comparing effort needed to move flap. There should be about an initial one quarter inch of low resistance to movement which corresponds to engine idle speed. After this position, flap tension should increase and be constant throughout remainder of movement range. There should be no roughness or tight spots. It is NOT possible to adequately test these airflow meters with an ohmmeter.
    3) Run engine up to normal operating temperature. Test emissions and idle CO adjustment with air bypass screw. IF CO adjustment is not possible, remove airflow meter cover and MARK current position of spring tension rachet with Tipp-Ex. INCREASE SPRING TENSION TO WEAKEN MIXTURE. DECREASE SPRING TENSION TO RICHEN MIXTURE. Do this one or two clicks at a time testing for CO adjustability each time - as soon as you can adjust CO with air bypass screw you are there! If you run into problems reset rachet to original position.

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