2015 Tahoe P0171 and P0174 Lean Both Banks - Hesitation on Accel

Question

My Chevy Tahoe has started stumbling when pulling away from stoplights and the check engine light just popped on for lean codes on both banks. I can hear a slight whistling sound from the engine bay when it is idling, but it goes away once I get moving. The fuel trims are sitting around +22% at idle but they drop back down toward normal when I hold the RPMs at 2500.

Jake Morrison · Accepted Answer

The issue was the PCV VLOM (Valley Cover) tube and a cracked intake manifold gasket on the rear of bank 2. I replaced the intake manifold gaskets with a Fel-Pro set (Part #MS97219) and installed a new PCV hose assembly (Part #12639611). I torqued the manifold bolts in two passes, ending at 89 lb-in, and the fuel trims returned to -2% at idle immediately. Total cost for parts was about $85 and took 3 hours.

backyard_bart · Answer

Grab a can of brake cleaner or a smoke machine if you have access to one. Spray around the intake runners and the PCV hoses; if the idle dips or changes, you found your leak source.

Brian O'Connor · Answer

Don't overlook the brake booster hose or the EVAP purge solenoid. If the purge valve is stuck open, it will pull unmetered air into the manifold and cause the exact lean condition you are describing.

Pete Sanders · Answer

Since your fuel trims improve at higher RPM, you almost certainly have a vacuum leak. Check the intake manifold bolts as they are known to snug up or the gaskets shrink over time on these EcoTec3 engines.

2015 Tahoe P0171 and P0174 Lean Both Banks - Hesitation on Accel

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