I know there have been many posts on this subject but I thought I'd share my experience.
I brought a 2004 Scenic Privilage 1.6DCI for my wife back in Feb and after a week it started to experience starting problems from hot or cold. It would take several attenpts for the car to start properly but once running it would be fine.
As the car was under warranty it was booked in to a local garage to investgate, i was fobbed off with the usual 'we checked the error codes and everthing is fine', 'bring it back if you still have a problem.....:loser::loser:
Low and behold, next day it was playing up again so I ordered and replaced the
sensor myself as recommended on this forum (£21.16). Apparently the warranty didnt cover sensors......
Since fitting the sensor the car has been transformed starting perfectly (three weeks since work done).
My advise would be if you have starting problems, change the sensor as a matter of course, chances are it'll fix it.