Idle Air Control (IAC) System Malfunction

NOTE: The following test procedures are for DTCs P1506.

Fig 1: Idle Air Control (IAC) System Malfunction Detection Condition Possible Cause

G03723741

Courtesy of MAZDA MOTORS CORP.

IDLE AIR CONTROL (IAC) SYSTEM MALFUNCTION INSPECTION/ACTION CHART

STEP	INSPECTION		ACTION
1	Was PCM Quick Test performed?	Yes	Go to next step.
1	Was PCM Quick Test performed?	No	Perform PCM Quick Test. See PCM QUICK TEST .
2	DTC P1506: CHECK FOR VACUUM LEAKS Key On, Engine Running (KOER). With the engine at idle, listen for vacuum leaks. Inspect the entire intake air system from the mass air flow (MAF) sensor to the intake manifold for damage or leaks such as: Cracked or punctured intake air tube. Loose or cracked IAC air tubes. Loose intake air tube at the air cleaner housing or throttle body. IAC valve assembly or gasket seal. Intake manifold assembly or gasket seal. EGR valve gasket seal. Vacuum supply connectors and hose. PCV valve, connectors and hoses Key OFF. Were any leaks detected?	Yes	Repair or replace components as necessary. Go to step 7.
2		No	Go to next step.
3	CHECK EVAP SYSTEM FOR A STUCK OPEN VALVE Disconnect hoses at EVAP vapor management valve. Connect hand vacuum pump at the fuel vapor port of EVAP canister at the EVAP vapor management valve. Apply 53 kPa (16 in-Hg) of vacuum to EVAP vapor management valve. Does EVAP vapor management valve hold vacuum for 20 seconds?	Yes	Reconnect all components. Go to next step.
3		No	Replace EVAP vapor management valve. See EVAPORATIVE EMISSION CANISTER PURGE VALVE . Go to step 7.
4	CHECK EVAP SYSTEM FOR A STUCK OPEN VALVE Key On, Engine Running (KOER). Bring engine to normal operating temperature. Transaxle in park or neutral. Disconnect IAC valve connector. Key OFF. Did the rpm drop or engine stall?	Yes	Go to next step.
4		No	Inspect throttle body for damage. If OK: Replace IAC valve. See IDLE AIR CONTROL (IAC) VALVE -- 2.3L or IDLE AIR CONTROL (IAC) VALVE -- 3.0L (4V) . If not OK: Repair or replace throttle body. See THROTTLE BODY for 2.3L engine or THROTTLE BODY for 3.0L engine. Go to step 7.
5	CHECK IAC CIRCUIT FOR SHORT TO GROUND Disconnect WDS or equivalent tester from DLC. Disconnect PCM. Install breakout box, leave PCM disconnected. Measure resistance between PCM test pin E39 (IAC) and PCM test pins C10 and C49 (PWR GND). Is resistance greater than 10K ohms?	Yes	For fast idle symptom currently present: Replace PCM. See POWERTRAIN CONTROL MODULE (PCM) . Go to step 7. All others: Go to next step.
5		No	Repair short in IAC SIG circuit. Go to step 7.
6	CHECK IAC SYSTEM FOR INTERMITTENT OPEN OR SHORT Connect WDS or equivalent tester. Key On, Engine Running (KOER). Using WDS or equivalent tester, select Diagnostic Data Link. Select PCM. Select PID/Data Monitor and Record. Access IAC PID and RPM PIDs. With engine at normal operating temperature, accessories off and at idle, the IAC duty cycle must be between 20% and 45%. Observe the PIDs for an indication of a fault while performing the following at idle: Lightly tap on IAC valve assembly and wiggle harness connector to simulate road shock. Grasp the vehicle harness closest to the IAC valve assembly. Shake and bend a small section of the harness from the IAC to the dash panel and from the dash panel to the PCM. Do the IAC or RPM PIDs suddenly change in value indicating a fault?	Yes	Isolate fault and repair as necessary. Go to next step.
6		No	For idle quality, starting or stalling symptoms currently present: Replace IAC solenoid. See IDLE AIR CONTROL (IAC) VALVE -- 2.3L or IDLE AIR CONTROL (IAC) VALVE -- 3.0L (4V) . Go to next step. All others: See TEST 3: INTERMITTENT with IAC and RPM PID data and list of possible causes.
7	VERIFY TROUBLESHOOTING OF DTCs COMPLETED Make sure to reconnect all disconnected connectors. Clear DTCs from PCM memory using WDS or equivalent tester generic OBD II function. Perform PCM Quick Test. See PCM QUICK TEST . Is same DTC present?	Yes	Replace PCM. See POWERTRAIN CONTROL MODULE (PCM) . Repeat PCM Quick Test. See PCM QUICK TEST .
7		No	If any other DTC is present, go to applicable DTC inspection. If no DTC is present, troubleshooting complete.