Ciera V6-173 2.8L VIN W FI (1986)
Engine idle speed can be adversely affected by the following:
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Park/Neutral Switch - If ECM thinks the car is always in neutral, then idle will not be controlled to the specified rpm when in drive range.
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Leaking injector(s) will cause fuel imbalance and poor idle quality due to excess fuel. See CHART A-7.
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Vacuum or crankcase leaks can affect idle.
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When the throttle shaft or throttle position sensor is binding or sticking in an open throttle position, the ECM does not know if the vehicle has
stopped and does not control idle.
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Check AIR management system for intermittent air to ports while in "Closed Loop".
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In addition to electrical control of EGR, be sure to examine the EGR valve for proper seating.
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Faulty battery cables can result in voltage variations. The ECM will try to compensate, which results in erratic idle speeds.
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The ECM will compensate for A/C compressor clutch loads. Loss of this signal would be most apparent in neutral.
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Contaminated fuel can adversely affect idle.
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Perform injector balance test CHART C-2A.
If all OK, refer to "Rough, Unstable, Incorrect Idle or Stalling", see Diagnosis By Symptoms - No Trouble Codes Stored.
