Diagnostic Aids

Any condition that can affect engine performance at idle, can affect performance of IAC system. A careful visual and/or physical inspection of engine is necessary when scan tool indicates engine speed or IAC Motor Command readings are out of range. A warm engine that is idling too slow, with a high IAC Motor Command of 50 percent or more, may have an open in Ignition Positive Voltage circuit to terminal No. 5. A warm engine that is idling too fast, with a low IAC Motor Command of 15 percent or less, may have an open in Ignition Positive Voltage circuit to terminal No. 2. An intermittent IAC system concern may be caused by poor electrical connections in IAC valve circuits. Thoroughly check any circuitry that is suspected of causing an intermittent condition. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES - TRUCKS article.