How can I fix sudden loss of accelerator function on my Focus 1.8Tdi ?

My Focus 1.8Tdi (W reg) cuts power to idle mode on longer runs (say >1hr.) never short journeys and yellow coil light illuminates. Power restored by switching ignition off and on again but then fault recurs soon after. This is a potentially dangerous problem and also seems to be very common. Has anyone else found Alison's solution to replace electronic accelerator to be effective?