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2002 Ford Expedition 5.4L Engine Running Poorly with P0171 and P0174 OBD2 Codes

Model: 02 Expedition 5.4 Fault Code: P0171 Posted: 2018-11-04 15:46

I'm new to forums and have no other options—my check engine light came on last year, triggering P0171 and P0174 diagnostic codes. My 2002 Ford Expedition with a 5.4L V8 engine runs very poorly in cold weather. The issue disappeared during the summer but has returned after temperatures dropped this morning. The truck now struggles to start and runs roughly, especially at idle. I'm hoping for some expert advice on how to diagnose and fix this. Any insights or troubleshooting steps would be greatly appreciated. Thank you in advance!

Related fault codes
P0171P0174
Comments (1)
Anonymous 2018-11-04 16:49

The symptoms suggest a possible vacuum leak, though it's not definitive. The most reliable way to identify the source is an intake manifold smoke test. While YouTube offers many DIY tips, using OBD2 live data—such as fuel trim readings at idle versus under load—can significantly reduce troubleshooting time by filtering out unlikely causes that don't show up in real-time data.