As a temporary fix I closed the EGR valve manually and left it disconnected. This allowed the vehicle to be driven in a nearly normal manner. My suspicion was that the driver device for the EGR valve motor was faulty. Unfortunately removal of the ECU is particularly difficult in this model being at the base of the A-pillar and behind security covers.The customer did not want to continue with further investigation and took it as it was. They told me they would rather spend the money on another vehicle as this was has always been troublesome.
Thanks for you help Job.
Shaun