Idle Air Control (IAC) System Diagnosis

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

Engine Controls Schematics: MAF, Secondary Air Injection Pump Solenoid, IAC and Secondary AIR Pump:

CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) controls the engine idle speed by adjusting the position of the Idle Air Control (IAC) motor pintle. The IAC is a bi-directional motor driven by 2 coils. The PCM pulses current to the IAC coils in steps, or counts, to extend the IAC pintle into a passage in the throttle body and decrease air flow. The PCM reverses the current pulses to retract the pintle and increase the air flow This method allows highly accurate control of the idle speed and a quick response to changes in the engine load.

DIAGNOSTIC AIDS
Use the J 35616-A connector test adapter kit for any test that requires probing the PCM harness connectors, electrical center fuse/relay cavities, component terminals or a component harness connector. Using this kit will prevent damage caused by improper probing of connector terminals. If the problem is intermittent, refer to Intermittent Conditions for diagnosis. Intermittent Conditions

Check for the following conditions:
^ A poor connection at the PCM or the IAC motor. Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connections.
^ A damaged harness. Inspect the wiring harness for damage.
^ A restricted air intake system. Check for a collapsed air intake duct, a restricted air filter element, or any foreign objects blocking the air intake system.
^ The throttle body. Check for objects blocking the IAC passage or the throttle bore, any excessive deposits in the IAC passage and on the IAC pintle, and any excessive deposits in the throttle bore and on the throttle plate.
Check for a sticking throttle plate. Also inspect the IAC passage for any deposits or any objects which will not allow the IAC pintle to fully extend.
^ A vacuum leak. Check for a condition that causes a vacuum leak, such as any disconnected or damaged hoses, any leaks at the EGR valve or at the EGR pipe-to-intake manifold, any leaks at throttle body, a faulty or incorrectly installed PCV valve, a disconnected intake manifold brake booster hose, etc.

Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
11. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read-only Memory (EEPROM). If the PCM is replaced, the new PCM must be programmed.