2006 Ford Escape XLT P0171 Code: System Lean Bank 1 - Low Fuel Efficiency and Rough Idle Issues
I recently purchased a 2006 Ford Escape with 106,000 miles from an auction. The vehicle had several engine modifications performed prior to sale. It is currently displaying a P0171 diagnostic trouble code indicating a system lean condition in Bank 1. I've already conducted multiple smoke tests on the intake system, which showed no leaks, and performed a catalytic converter snap test. Additionally, I replaced the Mass Air Flow (MAF) sensor. Despite these efforts, the P0171 code persists. Fuel efficiency has dropped to approximately 10.3 mpg—about half of what is expected for this model based on online references. The vehicle also exhibits a rough idle and occasionally shudders during operation. What could be causing this issue? Are there any other potential causes or diagnostic steps I should consider?
The previous mechanic suggested waiting for 200 miles of driving to allow the engine control module (ECM) to recalibrate, especially since the vehicle had been sitting for an unknown period. However, this seems unlikely as a standalone solution and may not resolve underlying issues. I'm considering getting a second professional opinion to verify the diagnosis and rule out any modifications that could have affected emissions or fuel delivery.