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DTC P0505 - Idle Control System Malfunction

NOTE: If DTC P1508 is set, trouble shoot DTC P0505 last.
  1. Start engine and run at 3000 RPM with no loads and transmission in Park or Neutral until radiator fan comes on. Allow engine to idle. Using OBD-II scan tool, ensure Throttle Position (TP) sensor indicates about 10 percent with throttle fully closed. Using OBD-II scan tool, ensure Engine Coolant Temperature (ECT) sensor indicates 194-205°F (90-96°C). If TP and ECT sensors are okay, go to next step. If TP and ECT sensors are not okay, repair suspect sensor circuits.
  2. Using OBD-II scan tool, check engine speed with no loads (headlights, blower motor, rear defogger, radiator cooling fan and A/C off). If engine speed is 650-750 RPM, problem is intermittent. System is okay at this time. If engine speed is 650 RPM or less, go to next step. If engine speed is 750 RPM or more, go to step 4).
  3. Disconnect IAC valve 3-pin connector located at middle of engine compartment. If engine speed does not decrease or engine does not stall, replace IAC valve. If engine speed decreases or engine stalls, adjust base idle speed. See ADJUSTMENTS article. If engine speed cannot be adjusted to specification, clean throttle body ports.
  4. Turn ignition off. Remove air intake duct from throttle body. Start engine and allow it to idle. Place a finger on upper port in throttle body. If engine speed does not decrease, check for vacuum leaks and ensure throttle valve is completely closed. Repair as necessary. If idle speed decreases, adjust base idle speed to specification. See ADJUSTMENTS article. If idle speed will not adjust to specification, replace IAC valve.
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