DTC P0505 - Idle Air Control (IAC) System Malfunction
- Turn all accessories off. Ensure ignition timing is set to specification. See ADJUSTMENTS
article. Connect scan tool to Data Link Connector (DLC). Start engine and allow to reach normal operating temperature. Select DATA LIST mode on scan tool. Ensure IAC duty is within specification. See IDLE SPEED/IAC DUTY SPECIFICATIONS
table. If idle speed and IAC duty are within specification, go to next step. If idle speed is high, stop engine and go to step 3). If idle speed is low, go to step 7). If idle speed is within specification but IAC duty is not, adjust to specification as described in step 6), then return to step 2).IDLE SPEED/IAC DUTY SPECIFICATIONS
A/C OFF RPM/IAC Duty (1) A/C ON RPM A/T: 750-850/3-20% 850-950 M/T: 700-800/3-20% 850-950 (1) For vehicles operating at high altitude (6560 Ft. or above), IAC duty should be approximately 30 percent. - With engine at idle, turn headlights on. If idle speed stays within specification, check for an intermittent problem. See TESTS W/O CODES article. If idle speed does not stay within specification, go to step 4).
- Start engine and allow to reach normal operating temperature. Select MISC. TEST on scan tool. Attempt to control idle speed with scan tool. If idle speed changes, go to step, 6). If idle speed does not change, go to next step.
- Turn ignition off. Disconnect IAC valve harness connector. Using an ohmmeter, measure resistance of opening coil and closing coil of IAC valve. See Fig 1 . If resistance is 18.8-22.8 ohms at 68°F (20°C), go to next step. If resistance is not as specified, replace IAC valve. Retest system.
- Using fused jumper wires, connect battery voltage to terminal No. 2 of IAC valve. Connect terminal No. 1 to ground. Open throttle valve and blow air int IAC valve hose. Air should flow through valve. Switch ground lead to terminal No. 3. Air should not flow through IAC valve. Replace IAC valve if it does not operate as specified. If IAC valve does operate as specified, check Red/White wire, Red/Yellow wire, or Red/Black wire between IAC valve and PCM for an open or short. Repair as necessary. If wires are okay, replace PCM. Retest system.
- If IAC duty was less than 3 percent in step 1), attempt to adjust idle speed and IAC duty using idle air adjusting screw. If adjustment cannot be obtained, check for false air entering intake system. Repair as necessary. If IAC duty was 3 percent or greater in step 1), check ECT sensor performance. See SYSTEM/COMPONENT TESTS article. Repair as necessary. If ECT sensor is okay, replace PCM. Retest system.
- Check IAC valve and circuit as described in step 3). If idle speed changes using scan tool, go to step 9). If idle speed does not change using scan tool, follow procedures in step 4). Replace IAC valve if operation is not as specified. If IAC valve operation is okay, go to next step.
- Check for an open in Red/White wire, or short to ground in Red/Yellow wire between IAC valve and PCM. Repair as necessary. If wires are okay, replace PCM. Retest system.
- If IAC duty was greater than 20 percent in step 1), attempt to adjust idle speed and IAC duty using idle air adjusting screw. If adjustment cannot be obtained, check for false air entering intake system. Repair as necessary. If IAC duty was 20 percent or less in step 1), replace PCM. Retest system.