I have heard allsorts of theorys on the lump idle it could be one of a number of faults . All it will take is mechanic to spend some time with your car using some test parts ie taking the known parts which cause this kind of problem off and putting other ones on ( test parts) and elimating the faulty parts . This takes time and the mechanics usually have so many vehicles booked in in one day they dont have time to do this .
When my car was a year old it went in under warrenty as it had really bad lumpy idle they couldnt get to the bottom of it so they kept it for two weeks in the end they rang one of these renault tech experts and replaced a relay or somthing . Since then I have never had a problem engine runs really steady .
What I have heard is that the fuel pressure reg on petrol renaults can go faulty after about 3-4 years causing the
to try keep altering fuel - air mixture causing lump idle .
This can also cause the problems with starting injector code faults and missfireing at high revs .
My friend who has had his
for 4 years has had this problem and was told injectors needed replacing by one renault garage I recommended him a different one they replaced the fuel pressure reg and he tells me its like driving a new car .
I am not saying this is the fault with your car it could be one of a number of things but you would have thought renault would have got to the bottom of this .
If I was you I would keep taking your car back and refuse to pay until they find the fault they are meant to be the experts also give
a call and explain your problems see what they can do after all there is a big push at the moment of keeping the customer happy with all these surveys top gear and the likes are doing