I have a 407 SE 2.0 2004 model, petrol, low milage (56,500). Great car for what I paid. I have had a problem with the fuel consumption since I purchased the car about 2 years ago. Fuel consumption seems to be very high, 350 miles from a tank max, even on a long trip, much less when city driving and when at idle you can feel the car jerking which seems to get worse the longer the cars is left to idle.

It's fine when running except for the low mileage. No smoke, no bad smells from the exhaust. I have had the engine management software update which seemed to help for a short while but back to square one in a few weeks. Coils, plugs, HT leads, fuel filter, checked and all is normal. CO2 levels are off the chart so will prob fail the next MOT unless its sorted.

Does anyone have any ideas on what it could be or what I could check next?