Cause
Leaking intake manifold gasket
Unmetered air entering where the manifold meets the head. A leak is a roughly fixed quantity against airflow that varies enormously, so it dominates at idle and fades under load — and it is often worst cold, before the gasket and casting have expanded to close the gap.
Typically a moderate job.
Codes this can cause (17)
Codes where this is a likely explanation first, rather than merely a possible one.
- P0507 Idle Air Control System RPM Higher Than Expected Likely for this code Moderate
- P2073 Manifold Absolute Pressure/Mass Air Flow — Throttle Position Correlation at Idle Likely for this code Moderate
- P2177 System Too Lean Off Idle Bank 1 Likely for this code Moderate
- P2179 System Too Lean Off Idle Bank 2 Likely for this code Moderate
- P2187 System Too Lean at Idle Bank 1 Likely for this code Moderate
- P2189 System Too Lean at Idle Bank 2 Likely for this code Moderate
- P219B Bank 2 Air-Fuel Ratio Imbalance Likely for this code Moderate
- P219F Cylinder 4 Air-Fuel Ratio Imbalance Likely for this code Moderate
- P21A0 Cylinder 5 Air-Fuel Ratio Imbalance Likely for this code Moderate
- P2279 Intake Air System Leak Bank 1 Likely for this code Moderate
- P2282 Air Leak Between Throttle Body and Intake Valves Likely for this code Moderate
- P0171 System Too Lean — Bank 1 High
- P0174 System Too Lean — Bank 2 High
- P2173 Throttle Actuator Control System — High Air Flow Detected High
- P21A1 Cylinder 6 Air-Fuel Ratio Imbalance Moderate
- P2339 Cylinder 4 Above Knock/Combustion Vibration Sensor Threshold High
- P2ADF Intake Air System Leak Bank 2 Moderate
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