safe mode zafira

hi guys, i got the cam sensor changed at a local garage, car ran fine for a day or so, then back to its juddery self. the garage also changed a faulty vaccum pipe, i changed the mass air flow meter and it ran pretty much perfect all day. did a 30 mile trip with no problems, then tonight i went out and engine was cutting out again. does anyone know how the air flow meter comes out of the pipe that its fastened into. i dont want to knacker the full thing. i thing now its time to look at the injectors or body housing, was going to replace mass air flow first though.