Hi. This seems to be a regular fault with lagunas. Mine did that when it was a few months old. Took Renault 2 years to find the fault. Turned out to be the front lambda sensor that was reading incorrectly. Renault decided the fix was to replace the rear sensor and increase the idle RPM limiter to compensate. When the front sensor was finally replaced the car ran better and I had to decrease the idle speed however im still having emission problems years later. I even purchased a Clip to help me out.
The reason Renault replaced the rear sensor was due to it not reading on the Clip software but this was because the
couldn't get a balance on readings from various sensors, for example front sensor said one thing and rear massively different, fuel mixture would adjust to compensate but then its running too lean/rich so it keys it back, eventually the
ignores the rear sensor disabling it and triggers an engine management fault light with fault for knackered CAT.
I think the reason im having issues is because Renault messed with other settings as well so its over fueling.
Replace the lambdas, Universal ones cost only around £18 and can be purchased off
. Front and rear are the same but access to the front can be quite difficult if you don't have the correct tools. As long as it is the 4 wire Zirconia sensor it should be ok.
Heres a link to Lambdas
Other faults could be
, Air intake sensor, Engine Temp sensor or a duff Catalytic converter. The sensors are fairly cheap and can be easily replaced at home with only a basic tool kit. Could also be an
valve but I doubt it.
Best of luck with it.