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

Question

My truck is idling really rough and the check engine light just popped 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, it feels like it wants to stall. I can hear a faint whistling sound coming from the top of the engine area when it is cold.

hd_trucker_77 · Accepted Answer

The issue was the intake manifold gaskets (Part #MS97091). I performed a smoke test and saw thick smoke pouring out from the base of the manifold near cylinders 5 and 7. I replaced the gaskets and the knock sensor grommets while I was in there. Torqued the manifold bolts in two passes to 44 lb-in then 89 lb-in. Fuel trims returned to +/- 3% immediately and the rough idle is gone.

Kevin Tran · Answer

Check your intake manifold gaskets. On these GM 5.3 engines, the orange silicone gaskets flatten out over time and suck in unmetered air, especially when the engine is cold and the plastic is contracted.

Lina Brooks · Answer

You should look at the freeze frame data for your Long Term Fuel Trims. If the trims drop back down toward zero when you increase the RPM to 2500, you definitely have a vacuum leak after the throttle body.

Jake Morrison · Answer

Don't rule out the EVAP purge valve. If it's stuck slightly open, it will pull vacuum from the tank and mess up your mixture. Try disconnecting the vacuum line to the purge solenoid and plugging it to see if your idle smooths out.

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

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