2002 megane cutting out at idle

[cyber-shot]

hi can anybody help my mate has a 2002 1.6 16v megane the problem is when you start it, it runs ok,for about 20 to 30 seconds the it just stops dead,but will restart instantly, but if you give it a good rev for a few seconds it doesnt cut out, same sometimes if the engine is hot, he has changed the flywheel censer,still the same, there is another prob after changing the oil the service indicator will not reset