DTC P0505 - Idle Air Control (IAC) System Malfunction
- Ensure idle speed and IAC duty are within specifications. See IDLE SPEED in ADJUSTMENTS - 1.8L article. If idle speed and IAC duty are within specifications, go to step 3). If idle speed is high and IAC duty is low, or idle speed is low and IAC duty is high, go to next step. If idle speed and IAC duty are high, or idle speed and IAC duty are low, replace PCM. Retest system.
- Adjust idle speed and IAC duty. If adjustments can be made with idle air adjusting screw, go to next step. If adjustments cannot be made with idle air adjusting screw, go to step 4).
- If idle speed remains within specification as headlights are turned on, check for an intermittent problem. See appropriate TESTS W/O CODES article. If idle speed does not stay within specification, go to step 6).
- Ensure engine is cold. With ignition off, remove idle air adjusting screw and check for clogged passage. Clean if necessary. If passage is okay, measure fast idle plunger. See Fig 1 . With engine coolant temperature at 77°F (25°C) or less, measurement "A" should be 1.048-1.078 in. (26.6-27.4 mm). Start engine and allow coolant temperature to reach 126-154°F (52-68°C). Ensure fast idle control cam does not contact cam follower lever. If operation is as specified, go to next step. If operation is not as specified, replace fast idle plunger. Retest system.
- Ensure intake system does not draw false air (vacuum leaks, air cleaner connections, etc.). Repair as necessary. If intake system is okay, go to next step.
- Ensure engine is at normal operating temperature. Turn ignition off. Remove Light Green/Black wire (terminal No. 24) from PCM harness connector "B", leaving PCM connector connected. Start engine and note idle speed. Turn ignition off. Reconnect wire to PCM connector. Using a fused jumper wire, backprobe Light Green/Black wire to ground. Start engine and note idle speed. If idle speed does not change, go to next step. If idle speed increased, system is okay.
- Turn ignition off. Disconnect IAC valve harness connector. Using an ohmmeter, measure resistance between terminals of IAC valve. If resistance is 11-14 ohms at 68°F (20°C), go to next step. If resistance is not as specified, replace IAC valve. Retest system.NOTE: Incorrect jumper connections made to IAC valve will result in damage. Ensure all connections are made correctly. DO NOT reverse leads during test.
- Start engine and note idle speed. Using fused jumper wires, connect battery voltage to terminal No. 1 and ground terminal No. 2 of IAC valve terminals. See Fig 2 . If idle speed increases, check IAC valve harness for an open or short circuit. If IAC valve harness checks okay, replace PCM. If idle speed did not change, replace IAC valve. Retest system.