I have a 2007 A180 CDI (with 7 G-tronic transmission) with about 15 000 miles on the clock. I have two questions and would really appreciate any feedback.

1. Ever since taking delivery of the car it has presented a peculiar behaviour pattern: when the ambient temperature is above about 29C the engine idles at about 1000 rpm (as opposed to about 700 rpm). This means that I have to brake harder to get the car to a full stop and sit at traffic lights and intersections with a car that want to charge off.
I have taken the car to various dealer on numerous occasions - both with it displaying the behaviour and without. Of course they hook it up to a computerised diagnostic system and if there is no fault recorded they tell you it's fine. At last I found one service manager to gave me a very technical and impressive sounding explanation about high gearbox oil temperatures needing to be cooled. This would be all good and well except for the fact that if the ambient temp is above about 29C the car will rev high even from a cold start. Any ideas? I have not met one other A-class owner who has experienced this behaviour.

2. I do 90% of my driving in a city. I drive fairly conservatively but still can't seem to get my average fuel consumption below 8.5 to 9 litres/100km. I think that this is fairly heavy for a diesel fuelled vehicle and is not much less that the 3-litre TDi 4WD pick-up that I used to drive. The claimed fuel consumption figures for this model are substantially lower than what I'm getting.