Symptoms
An air leak is one of the least tolerated issues with a fuel-injected engine. The air/fuel ratio must be precisely controlled to function correctly. Symptoms of an engine code P2279 may include:
- Illumination of the Malfunction Indicator Lamp (MIL) with diagnostic code P2279 set
- Stalling at idle
- “Hunting” or surging at idle
- Lack of power
- Dead spots during acceleration
- ECM sets additional codes such as engine misfire in cylinder number 1
- Engine “knocking” due to lean mixture
- Cherry-red exhaust manifolds from an overly lean mixture
- Hissing sound produced by the air leak
- Increased resistance in power brakes (harder pedal)
Potential Causes
Potential causes of this engine code may include:
- Leak between the engine side of the mass air flow sensor and the air duct
- Air duct leak on the engine side
- Leak at the intake air temperature sensor
- Leak at the throttle body
- Crack or leak in the intake manifold
- Disconnected or broken vacuum hose
- Poor fuel injector seal to the manifold
- Leaking brake booster vacuum hose
- Leak under the dashboard on a vacuum-operated device
- Stuck PCV valve
- Stuck oil filler cap
- Anything and everything connected to the intake manifold could potentially cause this scenario.
Diagnostic and Repair Procedures
- First, start the engine and open the hood. Listen for a hissing sound and trace it back to its source. Repair it if necessary. A heater hose held to your ear works well.
- Perform a propane test. Remove the nozzle from a propane torch and install a rubber vacuum hose. Start at the mass air flow sensor and work toward the intake manifold, directing a small amount of propane toward all suspected devices.
- There will be a dramatic change in idle speed when the leak source is located.
- Run the propane hose all around the air ducts leading to the throttle body and intake manifold.
- Check for an interior vacuum leak under the dashboard. Do not use propane; listen. Often, one of the vacuum motors for the HVAC doors has come loose.
NOTE: Be cautious when using unlit propane to find a leak; we are not responsible for any damage or injury that may result from its use! If you are unsure about using it, you can also spray carburetor/choke cleaner on suspected areas. Or, build your own smoke machine. There are alternatives to using propane.
Once the leak is detected and fixed, use a common code scanner to clear the code and reset the ECM.
This code may apply to any vehicle from 1996 onward, but it appears to be more common on Vauxhall, Saab, Honda, Acura, and VW.