Tech Tips (by ALLDATA): Explorer runs bad at low RPM

Vehicle: 2004 Ford Explorer, 4WD, V6-4.0L, VIN E, Automatic Transmission

Mileage: 149,998

Problem: The vehicle came into the shop because it was running poorly below 2,000 rpm and the malfunction indicator lamp (MIL) was ON.


Details: The owner had already replaced the mass airflow sensor, which did not fix the problem, so he brought the vehicle to the shop. The technician connected a scan tool and retrieved the following diagnostic trouble codes (DTCs):

  • P0171 System Too Lean Bank 1
  • P0174 System Too Lean Bank 2

Based on the lean codes and the rough running condition at idle and below 2,000 rpm, the tech inspected for leaking vacuum lines.

Confirmed Repair: The vacuum line rubber fitting between the canister purge valve and intake manifold was cracked and leaking. After replacing the damaged line fitting, the DTCs were cleared and a test drive confirmed that fuel trims remained under +5%. Smooth idle was restored. Fixed.