Incorrect Intake Airflow in 1.4 Cruze and Sonic
Posted to Technical Discussion Forum on 10/2/2016
11 Replies
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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