2013 Chevy Silverado P0171 and P0174 Lean Both Banks - Rough Idle

Question

My truck is idling really rough and the check engine light just came on with codes for both banks running lean. It seems to smooth out a bit once I get up to highway speeds, but at stoplights the RPMs dip and it feels like it wants to stall. I can hear a slight whistling sound from the engine bay but I cannot pinpoint it.

garagegrease · Accepted Answer

The issue was a cracked PCV fresh air pipe and leaking intake manifold gaskets. I replaced the gaskets with the updated Fel-Pro MS97210 set and swapped the brittle PCV hose. Total cost for parts was about $65 and took roughly two hours to teardown and reassemble. I torqued the manifold bolts to 44 lb-in on the first pass and 89 lb-in on the final pass in the proper sequence, and my long term fuel trims dropped back to a healthy +2%.

Sarah Thompson · Answer

You should check the fuel pressure at the rail. If your fuel pump is getting weak, you won't get enough volume at idle, though usually a failing pump shows up more under heavy load rather than at idle.

Chris Donovan · Answer

Take a can of brake cleaner or a smoke machine and check the intake bellows and the PCV hose. The Corrugated plastic PCV hoses on these GMT900 trucks crack all the time and will give you those exact lean codes.

Pete Sanders · Answer

Check your intake manifold gaskets. Those plastic manifolds on the 5.3L are notorious for the gaskets flattening out over time, especially in cold weather, causing a vacuum leak that disappears once the engine warms up and the plastic expands.

2013 Chevy Silverado P0171 and P0174 Lean Both Banks - Rough Idle

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