EGR is about prevention acid rains rather than the global warming. It, actually, increases CO2 emissions.
Please do not blame everything on the EGR valve. It may cause warning lights, but there can be many other causes. If you have the described problems do the following:
0! Download the workshop manual from our Links. There are several files with the names similar to "MR364MEGANE0.pdf".
0!! Familiarise yourselves with it.
0!!! Find the fault-finding algorithms based on customer complaints. The dealers follow them.
1. Basic checks including fuel consumption, oil consumption, oil level, visual inspection of everything under the bonnet, pay special attention to unusual noises, smells, spots of oil, inspect visually the turbo, air ducts, intercooler. Check the clear pipe to the fuel pump for bubbles. Check whether the cabin lights dim while starting the engine (battery check). Is there any smoke from the exhaust upon starting?
2. Make sure that the oil, oil filter, fuel filter and air filter are fresh. All filters must be OEM and the oil must be MB229.3/MB229.5 AND 0/5w40 or just RN0710 (for the cars without FAP). Try to recall if you used any dodgy petrol stations recently. Drain water from the fuel filter.
3. Locate and visually inspect the boost pressure and MAF sensors. Move the turbocharger control linkage by hand, it should move freely.
4. Check if the turbocharger control linkage moves within a few seconds after starting the engine.
5. Use ELM327 interface and ScanMaster (or similar) software in your laptop to (a) read the fault codes and then (b) continuously record the engine parameters while replicating the fault. I mean, drive the car with the laptop connected. Build the plots and post them here. The parameters can be verified by the manual.
6. If within the last 30k miles the EGR valve was not cleaned, there is a good chance that you will have to do it anyway.
Without this and without knowing the history of the car (services, faults, repairs, type of journeys) it very difficult to help. Describe in great detail how the fault can be replicated.
(no, a different AlexB)