Idle Control System RPM Lower Than Expected
The engine is running at an idle speed lower than the PCM expects, typically below 600 RPM. This code indicates the idle air control system is not maintaining proper idle speed, which can result from vacuum leaks, intake restrictions, PCV valve issues, or throttle body problems.
What You Might Notice
- Rough or unstable idle
- Lower than normal idle RPM
- Check engine light illuminated
- Engine may stall at stops
- Hesitation when accelerating from a stop
Most Common Causes
- 1
Vacuum leak
Unmetered air entering the intake after the mass airflow sensor disrupts the fuel mixture and causes the engine to run lean, lowering idle speed.
- 2
Dirty or faulty throttle body
Carbon buildup or sensor malfunction in the throttle body prevents proper idle air control and airflow regulation.
- 3
Failed PCV valve
A stuck or damaged positive crankcase ventilation valve creates improper crankcase pressure and affects idle control.
- 4
Intake air restriction
A clogged air filter or blocked intake passage reduces airflow and causes the engine to run too lean at idle.
How to Diagnose It
- 1
Check Vacuum leak — Unmetered air entering the intake after the mass airflow sensor disrupts the fuel mixture and causes the engine to run lean, lowering idle speed.
- 2
Check Dirty or faulty throttle body — Carbon buildup or sensor malfunction in the throttle body prevents proper idle air control and airflow regulation.
- 3
Check Failed PCV valve — A stuck or damaged positive crankcase ventilation valve creates improper crankcase pressure and affects idle control.
- 4
Check Intake air restriction — A clogged air filter or blocked intake passage reduces airflow and causes the engine to run too lean at idle.
How to Fix It
- 1
Inspect for vacuum leaks
Check all vacuum hoses, brake booster line, and intake manifold gaskets for cracks, disconnections, or deterioration. Use a smoke test or listen for hissing sounds to locate leaks.
- 2
Clean or replace throttle body
Remove and clean the throttle body with throttle body cleaner to remove carbon deposits, or replace if the throttle position sensor is faulty.
- 3
Replace PCV valve
Remove the old PCV valve and install a new one to restore proper crankcase ventilation and idle control function.
- 4
Replace air filter and check intake
Install a new engine air filter and visually inspect the intake tract for blockages or obstructions that may be restricting airflow.
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