I have had my MG's head gasket skimmed and.

Hi I have had my mg's head gasket skimmed and replaced recently by a proper mechanic/garage her took it for a test run and he said it was cutting out on him, so I said ok what is the problem he then got a electrical engineer to look at it and diagnose the problem which he said it is the lambda sensor, injectors and inlet-manifold need replacing. This is where I am now feeling im be taken for a ride as I always thought the inlet manifold wasnt electrical only the injectors where is this true? As I have already paied enough and now I am getting very anoyied as he has had my car for just under a month now please help?