6 months ago, i had the same problem..
i went to Renault they told me "the spark plugs are the problem; they are not generating enough spark"... so, i used new ones and the same problem still exists. others told me belts, battery, ect...
anyhow, i've been through many attempts.. Finally, Renault, told me that i have to change some kind of a
coil (circulated in the picture in white) which is directly over the spark plugs. you have 4 coils over 4 spark plugs.
so, Renault tested the 4 coils (how? taking each of the 4 coils upward a little bit like half way, if it vibrates well then its ok, if not, it needs to be replaced!). two of the coils were vibrating weakly, consequently, Renault told me to replace all of the 4 coils, because "if one is not working well, others will come along", "why" i asked, they told me,
"lifetime of the coils" although my car is 04 1.6 60,000km only.
thanks god it works properly now..
https://img525.imageshack.us/img525/1474 ... noles4.jpg