Engine trouble and crap mpg

[Ant-172]

Had the car a year now an it's ran absolutely fine till the start of the week so it's not timing etc. When I first start it, it's idling at about 1200 ( it's never idled this high since I've owned it), once it gets to temp it does the total opposite and idles at about 500 and keeps cutting out, it's sounds really rough when idling, but drives as usual ie accelerates as it should but my usual mpg is roughly between 36/40 and this week it's been averaging 20mpg

any idea what it could be ?

 

[MartinR]

Colder air

 

[Cookson]

Lamba gone down?

 

[Gandi69]

I had a similar issue but not as severe, was only getting 24/25mpg using Vpower which is usually very good for me. Changed the front lambda and its up in the low 30s now even with a spirited drive here and there

 

[TheEvilGiraffe]

ICV (idle control valve) perhaps ?

Swap the lambdas front to rear as an 'easy' fix .. if that doesn't do it .. clean/replace the ICV.

Failing that ... er......................

Check the usual things .. ignition = coilpack / HTs / plugs.

 

[Ant-172]

Thanks for the replys guys, I'll try the lamba front to back etc hopefully that's what it is
i can't see it been plugs, they were only changed about 3000mile ago, I've tryed the coil pack and leads off my mates car and was still the same

i'll let you guys no if any of the above do the trick, if it is either one, what prices am I looking at for both, cheap fix ?

 

[Ant-172]

It was intact the lambda sensors guys, fitted 2 Bosch ones this afternoon, (got them both from euro car parts while they had the 31% off deal online) mpg's back to normal and no lumpy idle anymore.
one last question thou, the emissions light has stayed on, will this go off by itself or do I need to have it knocked off ?

 

[stevo123]

It was intact the lambda sensors guys, fitted 2 Bosch ones this afternoon, (got them both from euro car parts while they had the 31% off deal online) mpg's back to normal and no lumpy idle anymore.
one last question thou, the emissions light has stayed on, will this go off by itself or do I need to have it knocked off ?

IIRC the light will turn off after half a dozen fault free trips. If not renault will be able to do it for you.

 

[Ant-172]

Cheers mate, hopefully knock itself off soon then