2015 Silverado 1500 P0171 and P0174 - Rough idle and stalling at stops

Question

My truck is throwing both lean bank codes and it struggles to stay running when I come to a complete stop. It feels like it wants to die unless I give it a little gas in neutral. I can hear a slight whistling sound from the engine bay when it is idling in my driveway.

road_rambler · Accepted Answer

The issue was the PCV VLOM (Valve Lifter Oil Management) cover assembly hose which had a literal split in the plastic underneath the foam insulation. I replaced the PCV tube assembly (Part #12639698) which cost about $25. After swapping the hose and clearing the codes with my scan tool, the long-term fuel trims dropped back to +/- 3% and the stalling stopped immediately.

Megan Rivera · Answer

Check the intake manifold bolts. They are known to vibrate loose over time on the GM trucks, causing a leak at the mounting flange that the gaskets can't take up.

Marcus Bell · Answer

Check your fuel trims at idle versus 2500 RPM. If the trims improve at higher RPM, you definitely have a vacuum leak somewhere behind the MAF sensor.

Sam Holloway · Answer

On these EcoTec3 engines, the brake booster vacuum line or the PCV tube are common failure points. Use some soapy water or a smoke machine to find the leak.

2015 Silverado 1500 P0171 and P0174 - Rough idle and stalling at stops

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