I have a 2005 2.0 zetec M/T. When i am cruising at part throttle, then engine bucks at times. If I rev the engine to about 2500 RPM's and hold the pedal there, the engine RPM will evetually fall to about 1300 and slowly rise again. I have no codes and the check engine light is not on. The car is well maintained. I also have a OBD2 bluetooth scan tool and the torque app. Fuel pressure according to the app is just under 40 PSI. Im thinking it is the fuel pressure sensor on the rail. How can I verify?