Guide step
Visual inspection first
Check intake boots, PCV hoses, brake booster line, and manifold gasket areas.
Guide page
Vacuum Leak Checklist for Lean Codes and Rough Idle
A practical inspection sequence for intake leaks behind lean condition and idle quality complaints.
Guide step
Use trim behavior as a clue
If lean trim improves off idle, intake leaks become more likely.
Guide step
Smoke if needed
Smoke testing saves time when no obvious split hose is visible.
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Related codes
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P0171 — System Too Lean (Bank 1)P0174 — System Too Lean (Bank 2)P0101 — Mass Air Flow Circuit Range/PerformanceP0507 — Idle Control System RPM Higher Than ExpectedP0130 — O2 Sensor Circuit (Bank 1 Sensor 1)P0131 — O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1)P0133 — O2 Sensor Circuit Slow Response (Bank 1 Sensor 1)P0134 — O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 1)P0170 — Fuel Trim Malfunction (Bank 1)P0173 — Fuel Trim Malfunction (Bank 2)P2187 — System Too Lean at Idle (Bank 1)P2189 — System Too Lean at Idle (Bank 2)P0030 — HO2S Heater Control Circuit (Bank 1 Sensor 1)P0031 — HO2S Heater Control Circuit Low (Bank 1 Sensor 1)P0032 — HO2S Heater Control Circuit High (Bank 1 Sensor 1)P0050 — HO2S Heater Control Circuit (Bank 2 Sensor 1)P0051 — HO2S Heater Control Circuit Low (Bank 2 Sensor 1)P0052 — HO2S Heater Control Circuit High (Bank 2 Sensor 1)P2279 — Intake Air System LeakP051B — Crankcase Pressure Sensor Circuit Range/PerformanceP0556 — Brake Booster Pressure Sensor Circuit Range/PerformanceP0557 — Brake Booster Pressure Sensor Circuit LowP2177 — System Too Lean Off Idle Bank 1P2179 — System Too Lean Off Idle Bank 2P1101 — Mass Air Flow Sensor Out of Self-Test RangeP0069 — Manifold Absolute Pressure - Barometric Pressure CorrelationP0558 — Brake Booster Pressure Sensor Circuit HighP0559 — Brake Booster Pressure Sensor Circuit Intermittent
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Related symptoms
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