An A320 Captain elected to return to his departure airport following receipt of an ENG 2 FADEC Sensor Fault ECAM message the resolution for which included the caution to 'avoid rapid THR (thrust) changes.' He then enumerated his reasons for opting to return to his VFR departure airport.

Narrative

During cruise at FL350 we received an ECAM: Engine 2-FADEC B Fault; Sensor Fault; avoid rapid Thrust Changes. I contacted Dispatch and Maintenance and after a conference; decided to return to our departure airport for the following reasons: If we lost the other channel; the next step required that we land at the nearest suitable airport. Another concern was the potential loss of the left engine; which would leave us with only a degraded number 2 engine with the thrust change caution. On a single engine; we would very possibly require rapid thrust changes during certain phases of flight (approach; go-around). Continuing to our destination would have found us flying over higher; more mountainous terrain with fewer suitable alternate airports. I felt the safest option was to return to our departure airport with great VFR weather; and light winds.After an uneventful landing; a Maintenance Technician informed me that neither A or B FADEC channel was testing properly for engine 2; and both channels were testing normally for engine 1. He also informed me the FADEC had a history and had been worked on the previous evening. Our Flight Papers had no record of this maintenance in our Log History; despite the importance of the critical engine component. An additional concern is that our Flight Manual does not include the caution to Avoid Rapid Thrust Changes. In the event of an incomplete ECAM message it would be important for the flight crew to be aware of this operational precaution.