1996 Mercury Cougar 3.8L P1151 Code: Mass Air Flow Sensor Issue and Engine Stalling Fix
I recently connected my 1996 Mercury Cougar with a 3.8L engine to an OBD2 scanner, which detected fault code P1151. This code is associated with the mass air flow (MAF) sensor, indicating a lean condition in the engine's air-fuel mixture. I replaced the MAF sensor as recommended, but after starting the car, it runs smoothly for about one minute before beginning to stall. While driving, I have to press both the brake and accelerator pedal to keep it running. At times, the vehicle will run well for a short period, then suddenly become unstable, only to stabilize again once I reach a moderate speed. The issue seems intermittent. Does anyone know what could be causing this behavior or how to properly diagnose and fix it? I'm especially concerned about whether the P115 or MAF sensor replacement was sufficient or if there are other underlying issues related to the engine's air-fuel system.
P1151 indicates a lack of signal from the upstream O2 sensor (HO2S21), which suggests a lean condition in the exhaust. Given the age and model of your 1996 Mercury Cougar, this is most likely pointing to a faulty oxygen sensor on the passenger side, upstream of the catalytic converter. For reliable results and proper calibration, it's recommended to replace the sensor at a dealership rather than using aftermarket parts.