2013 Chevy Silverado P0171 and P0174 Lean Both Banks - Rough Idle

Question

My truck is idling really rough and the check engine light just popped on with codes for both banks running lean. It seems to smooth out a bit once I get up to highway speeds, but at stoplights it feels like it wants to stall. I can hear a slight whistling sound coming from the top of the engine but I can't pin it down.

torque_terry · Accepted Answer

The issue was a cracked PCV fresh air tube and a leaking Intake Manifold Gasket set. I replaced the gaskets with the updated Fel-Pro MS97204 Teal gaskets and installed a new PCV hose assembly (Part #12675675). I torqued the manifold bolts in two passes, ending at 89 lb-in, and the long-term fuel trims dropped back to a healthy +2%. Total cost for parts was about $85 and took 3 hours of labor.

turbo_tony · Answer

Grab a can of brake cleaner or a smoke machine. With the engine running, spray around the intake snorkel and the vacuum lines; if the RPMs dip or spike, you found your leak. Don't forget to check the EVAP purge solenoid as well.

shoptech_carlos · Answer

You should check your fuel pressure at the rail. If your fuel pump is starting to fail and can't maintain 55-60 PSI, you will lean out under load, although usually that shows up more at high RPM than at idle.

Lina Brooks · Answer

Check your intake manifold gaskets. These Vortec engines are notorious for the plastic intake manifold gaskets flattening out over time, especially in colder weather, which allows unmetered air to enter the combustion chamber.

2013 Chevy Silverado P0171 and P0174 Lean Both Banks - Rough Idle

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