Toyota Avensis Throttle Body Problems

The ECU and throttle body has been checked and no problems found. So why even after reaching normal running temperature does it idle at 1600rpm ? Its a T4 as model type.

Had 3 garages look at it. the last one was a Toyota specialist in Chelmsford. after 4 weeks and checking everything, including recommendation's from Toyota technical, they still cant solve the problem. Things checked/renewed were ECU unit...