Astra J System Too Lean Due to Integrated PCV Valve Failure

The most common cause for an excess oxygen condition in the Astra J, particularly the 1.4L Turbo (A14NET), is a failure of the integrated PCV valve within the valve cover. To confirm this, perform a smoke test on the intake system to check for leaks around the valve cover gasket or PCV ports. Additionally, inspect the valve cover for signs of diaphragm rupture, which allows unmetered air to bypass the intake system and enter the combustion chamber.

Sources