Cause
Disconnected or leaking vacuum hose
A hose split, perished or knocked off, letting unmetered air into the engine. A leak is a roughly fixed quantity against an airflow that varies enormously, so it dominates at idle and fades as the throttle opens — and rubber goes hard with heat and age, so the split is often only open when cold.
Typically an easy fix. Often worth checking before paying anyone to look.
Codes this can cause (39)
Codes where this is a likely explanation first, rather than merely a possible one.
- P0401 Exhaust Gas Recirculation A Flow Insufficient Detected Likely for this code Moderate
- P0525 Cruise Control Servo Control Circuit Range/Performance Likely for this code Low
- P0556 Brake Booster Pressure Sensor Circuit Range/Performance Likely for this code High
- P0A14 Engine Mount A Control Circuit/Open Likely for this code Low
- P0AB6 Engine Mount B Control Circuit/Open Likely for this code Low
- P2008 Intake Manifold Runner Control Circuit/Open Bank 1 Likely for this code Moderate
- P2011 Intake Manifold Runner Control Circuit/Open Bank 2 Likely for this code Moderate
- P2070 Intake Manifold Tuning Valve Stuck Open — Bank 1 Likely for this code Moderate
- P2071 Intake Manifold Tuning Valve Stuck Closed — Bank 1 Likely for this code Moderate
- P2143 Exhaust Gas Recirculation Vent Control Circuit/Open Likely for this code Moderate
- P2145 Exhaust Gas Recirculation Vent Control Circuit High 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
- P2260 Secondary Air Injection System Control B Circuit High Likely for this code Moderate
- P2261 Turbocharger/Supercharger Bypass Valve A — Mechanical Likely for this code Moderate
- P2279 Intake Air System Leak Bank 1 Likely for this code Moderate
- P2281 Air Leak Between Mass Air Flow Sensor and Throttle Body Likely for this code Moderate
- P2282 Air Leak Between Throttle Body and Intake Valves Likely for this code Moderate
- P2441 Secondary Air Injection System Switching Valve Stuck Closed Bank 1 Likely for this code Moderate
- P2443 Secondary Air Injection System Switching Valve Stuck Closed Bank 2 Likely for this code Moderate
- P2525 Vacuum Reservoir Pressure Sensor Circuit Likely for this code High
- P2526 Vacuum Reservoir Pressure Sensor Circuit Range/Performance Likely for this code High
- P2528 Vacuum Reservoir Pressure Sensor Circuit High Likely for this code High
- P2C90 Crankcase Ventilation System - Hose A Disconnected Likely for this code Moderate
- P2C91 Crankcase Ventilation System - Hose B Disconnected Likely for this code Moderate
Information, not instruction
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