2015 Chevy Silverado 1500 - Rough Idle and P0171 Lean Bank 1

Question

My truck started idling really rough at stoplights and the check engine light just popped on. It feels like it wants to stall but smooths out once I'm up to highway speeds. I can hear a slight whistling sound coming from the engine bay when it's idling in the driveway.

obd2_owl · Accepted Answer

It turned out to be the PCV diaphragm inside the driver side valve cover. I performed a smoke test and saw smoke pouring out of the small vent hole on the back of the cover. I replaced the entire driver side valve cover assembly (GM Part #12642655) which cost about $110. Torqued the bolts to 89 lb-in and the fuel trims returned to normal immediately. No more whistling or rough idle.

Carlos Diaz · Answer

Check your short term fuel trims at idle using a scan tool. If they are high at idle but drop down when you hold the RPMs at 2500, you definitely have a vacuum leak. Common spots on these L83 engines are the intake manifold gaskets or a cracked PCV hose.

Chris Donovan · Answer

Check the valve cover. The PCV valve is integrated into the driver side valve cover on these models and the internal diaphragm is known to rupture, which sucks unmetered air directly into the intake.

garagegrease · Answer

That whistling sound is a huge giveaway. Spray some brake cleaner around the intake manifold runners while the engine is running; if the RPMs dip or spike, you found your leak. Also check the evap purge valve as they can stick open and cause a lean condition.

2015 Chevy Silverado 1500 - Rough Idle and P0171 Lean Bank 1

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