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Corolla, Land Cruiser & Tercel

  1. Warm up engine and check ignition timing at idle. Disconnect vacuum hose from distributor sub-diaphragm and plug hose end.
  2. Check that ignition timing remains stationary for more than 1 minute. Stop engine and reconnect hose to check valve.
    Fig 1: High Altitude Compensation System (Corolla, Land Cruiser & Tercel)
    G38380Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
  3. Disconnect 2 hoses on top of HAC valve. Blow air into each hose and check that air flows into carburetor. Reconnect hoses to proper locations.


  1. Warm up engine and disconnect vacuum hose between HAC valve and distributor at HAC valve side, and plug hose end. Disconnect vacuum hose from distributor sub-diaphragm, and plug hose end.
  2. Check ignition timing; timing should be 5° BTDC. Reconnect hose to distributor sub-diaphragm. Check ignition timing; timing should be about 13° BTDC.
  3. Disconnect vacuum hose from check valve at Black side and plug hose end. Check that ignition timing remains stationary for more than 1 minute. Stop engine and reconnect hoses to proper location.
  4. Disconnect 2 hoses on top of HAC valve. Blow air into each hose and check that air flows into carburetor. Reconnect hoses to proper locations.