2015 Tahoe - P0171 Lean Bank 1 and Rough Idle at Stop

Question

My dash threw a CEL yesterday and the truck is stumbling pretty hard when I am sitting at red lights. It seems to clear up once I get moving on the highway, but the fuel trims are sitting at +20% at idle. I am worried about burning a valve if I keep driving it like this.

backyard_bart · Accepted Answer

The issue ended up being a cracked intake manifold gasket on cylinders 1 and 3. I performed a smoke test and saw vapor pouring out from the flange area. I replaced the gaskets with a new AC Delco set (Part #12626354) and torqued the manifold bolts to 89 lb-in in the correct sequence. Total part cost was about $45 and it took me two hours; fuel trims are now back to within 3 percent.

Chris Donovan · Answer

You should check your intake manifold bolts. These 5.3 engines occasionally have the bolts back out slightly or the gaskets flatten out, causing a lean condition that the computer can't compensate for at idle.

road_rambler · Answer

Don't rule out a faulty high-pressure fuel pump (HPFP) or a leaking injector, though usually a failing pump would give you a P0089 or low pressure code along with the lean lean bank.

Rachel Nguyen · Answer

Since your trims improve at higher RPM, you almost certainly have a vacuum leak. Check the PCV hose where it connects to the intake; those plastic lines get brittle and crack frequently on the EcoTec3 engines.

2015 Tahoe - P0171 Lean Bank 1 and Rough Idle at Stop

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