Hopefully i can help..
What Renault model / Year and Engine size do you have?
Any warning lights on since or prior to the issue?
Any unusual noises from the engine itself during cold start etc?
Hi..there sorry for the delay..thanks for your reply..
Ok..Firstly i doubt an engine flush will help with issue to be honest wither that be oil system flushed or coolant - engine service may help but i cant see it though if you did have the sparkplugs changed when the new coils where fitted if they are genuine coils then you shouldnt have issue with them - usually the most common failures you find on these in regards to cutting out is usuallly down to either crank or cam sensor itself loosing signal and thus obviously the engine will cut out so those two things certainly need to be checked - crank sensor is usually the most common sensor to fail so it maybe worth try a new one genuine sourced if possible another could be failing etc sensor pretty much an electronic choke in which monitors the temp of the coolant to help the ecu trim fuel air mixture so maybe worth looking into that too.aswell as that have the throtle body checked or cleaned out too sometimes these can carbonise up and cause all sorts of running issues cutting out etc so again certainly consider having that done.also seeing as you do have vvt engine you will have variable valve timing system dephaser pulley on the intake camshaft on that so certainly carefully listen for any rattle or unsual noises emitting from the timing side of the engine - if there is any such noise during cold startfrom that side that would certainly verify the dephaser at fault and causing the cutting out - one other option too would be to hook up a suitable diagnostic machine depending on it capability via live data might actually help pin point the which sensor is at fault...I do hope this helps