Idle Control System Malfunction (P0505)
The P0505 code indicates a malfunction in the idle control system, which manages engine idle speed by controlling airflow through the idle air control (IAC) valve or electronic throttle body. The powertrain control module (PCM) detects that the actual idle speed deviates from the target idle speed by more than a calibrated threshold, or that the idle control system is unable to maintain proper idle. This can be caused by a faulty IAC valve, vacuum leaks, throttle body issues, or wiring problems.
01. Most Common Causes
- Faulty idle air control (IAC) valve
- Vacuum leaks (intake manifold, hoses)
- Dirty or carbon-fouled throttle body
- Faulty throttle position sensor (TPS)
- Wiring or connector issues in the IAC circuit
02. Symptoms You Will Notice
- Erratic or unstable idle speed (too high or too low)
- Engine stalling, especially when coming to a stop
- Check Engine Light illuminated
- Poor fuel economy
- Rough idle or hesitation
03. Step-by-Step Diagnosis
Step 1: Scan for additional codes and check freeze frame data.
Step 2: Inspect vacuum hoses and intake system for leaks using a smoke machine or propane enrichment.
Step 3: Clean the throttle body and IAC valve with throttle body cleaner.
Step 4: Test the IAC valve resistance and operation with a multimeter or scan tool bidirectional control.
Step 5: Check wiring and connectors for damage, corrosion, or loose connections.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as the engine may stall unexpectedly, leading to a safety hazard. Short trips to a repair shop are acceptable if the idle is manageable.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for cleaning the throttle body and IAC valve, or up to $300-$500 if the IAC valve or throttle body needs replacement, including labor.