Check output from alternator . Check all earth points from engine to body and that the battery conections are clean , tight and greased up. For the radio to go off this points to earth problems. Is the battery fully charged up . Another thing is the regulator in the alternator the brushes could be worn down . After these checks .Remove and clean the air control valve .Just remove the plug on the back remove 2 screws and clean it ou.t with white spirits .Dont put it in to the fluid as it electrical parts inside will get damaged