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Est Emission System Check

  1. With shift lever in "P" (auto. trans.) or Neutral (man. trans.), run engine at fast idle and note timing change as test terminal is grounded. If timing changes, system is operating properly.
  2. If timing does not change on vehicles equipped with manual transmissions, proceed to step 3. If timing does not change on vehicles equipped with automatic transmissions, let engine return to idle and place transmission in "D". Note timing change as test terminal is grounded. If timing changes, system is operating properly.
  3. On all models, if there are no change in timing, check voltage at output of MAP (Manifold Absolute Pressure) sensor or vacuum sensor as vacuum hose is removed and reinstalled. If no change occurs, problem is in the vacuum or MAP sensor circuit. If voltage output changes, proceed to step 4.
  4. Disconnect park/neutral switch and recheck for timing change. If timing changes, problem is either an improperly adjusted or faulty park/neutral switch. If timing does not change, check for grounded wire from terminal "H" of ECM to park/neutral switch. If wire is not grounded, replace ECM.
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