2015 Chevy Silverado P0171 and P0174 Lean Both Banks - Rough Idle

Question

My truck started idling really rough at stoplights and the check engine light just popped on. If I give it gas while driving it seems to smooth out okay, but it feels like it wants to stall when stopped. Scanned it and got lean codes for both bank 1 and bank 2.

Lina Brooks · Accepted Answer

Found the issue using a smoke machine. The intake manifold gaskets were leaking badly at the rear of the engine. Replaced the gaskets with a new AC Delco set (Part #12626354) and torqued the manifold bolts to 89 lb-in. The job took about 3 hours and cost $45 in parts, and the fuel trims are back to +/- 3% now.

Megan Rivera · Answer

Could be a failing high pressure fuel pump (HPFP) failing to maintain rail pressure, but usually that triggers a P0087 code as well. I'd stick to looking for vacuum leaks first.

Pete Sanders · Answer

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

Greg Walters · Answer

Look closely at the intake bellows (the rubber boot) between the filter box and the throttle body. These often crack in the accordion ribs and let unmetered air in, causing lean conditions on both banks.

2015 Chevy Silverado P0171 and P0174 Lean Both Banks - Rough Idle

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