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

Question

My Tahoe just started idling really rough and threw a CEL for lean codes on both banks. I notice a whistling sound coming from the engine bay when I step on the gas, and it feels like it wants to stall at red lights. The fuel trims are sitting at +25% at idle but get better when I increase the RPMs.

Marcus Bell · Accepted Answer

The issue was a ruptured PCV diaphragm integrated into the driver-side valve cover. I performed a smoke test and saw smoke pouring out of the small vent hole on the valve cover. I replaced the entire valve cover assembly (Part #12659640) which includes the new gasket and PCV valve. The part cost about $115 and took an hour to swap; fuel trims are back to +/- 3% and the whistle is gone.

torque_terry · Answer

Have you checked the PCV tube? These EcoTec3 engines are known for the plastic PCV lines cracking right where they clip onto the valve cover or intake manifold.

dieselmike88 · Answer

Since the fuel trims improve at higher RPMs, you definitely have a vacuum leak. Check the intake manifold gaskets or the brake booster line for cracks.

Sarah Thompson · Answer

Try spraying some brake cleaner around the intake manifold while the engine is running. if the idle stumbles or smooths out, you found your leak point.

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

Suggest a repair