03 renault megane dynamique 1.4ltr?

Shes a beauty of a car to drive but it has problems when she stars up, car starts and struggles to keep goin unless i put my foot on the gas. Like i can hear the engine struggle and ofcourse renault cant sort the problem (renault cant sort there own technology). So has anyone had a simular problem with there car at any stage??? Be great to get a reply or advice on the matter!! O its the renault with the push 'start' button