There are some problems with incorrect and/or unmetered intake airflow in Cruze and Sonic vehicles with the 1.4 turbo engine. They usually result in a rough idle with P0171 set or with no driveability complaints and P1101 set.

If you see one with a rough idle and P0171 set, check the orifice in the PCV cap in the valve cover for drawing air at idle. If you put your finger over the orifice, you will feel vacuum and the idle will smooth out. Replacing the valve cover may only be a temporary fix unless you look for the cause. Pull the PCV tube from the intake manifold and look into the port for a small orange cone shaped valve protruding on the firewall side.

Enlarge this picture and you will see a correct valve protusion.

[2012 Chevrolet Cruze LT, ECM/Inputs/Outputs Scan Data]

If the composite valve is missing, it has been sucked through the engine and spit out the exhaust usually with no other damage. Without this non-return valve present, excessive vacuum has damaged the diaphragm in the PCV cap. Installing just a new valve cover alone will result in another diaphragm failure. The proper fix is to replace the valve cover, PCV tube and intake manifold as the non-return valve is not serviced separately.

If, instead, you see a P1101 set with no other complaints, first check the throttle opening percentage.

[2012 Chevrolet Cruze LT, ECM/Inputs/Outputs Scan Data]

At idle, the throttle opening should read over 8% on the scanner. This vehicle read only 2.8% at best.

[2012 Chevrolet Cruze LT, ECM/Inputs/Outputs Scan Data]

In this case, pull the PCV tube from the intake and either plug or tape the port in some manner. Restart the engine and recheck the throttle position.

[2012 Chevrolet Cruze LT, ECM/Inputs/Outputs Scan Data]

A good position averages over 8%. A lower position shows unmetered air flow into the throttle body. This vehicle ran between 8 - 12% with the port blocked. In this case, replace the PCV tube only and retest. The tube has an internal slide valve on the throttle body end that can stick open and cause excessive air flow.

If the air flow on a Cruze is normal with a P1101 set, remove the air cleaner lid and check that the diffuser has not fallen off on top of the air filter.

James from Florida

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