I have recently taken delivery of a new Jaguar XF 2.2d and find it a very comfortable motorway cruiser, if a little underpowered but manage 45mpg at a push. One feature that I am having difficulty with is the Eco-Drive. I live in London and often use the M25 with its constant stop start traffic when the Eco-Drive is switching the engine on and off constantly until I disable it. I also find the same problem in heavy local traffic. There is a slight delay with the Eco-Drive so pulling out into traffic can be a bit dangerous at times. As the system defaults to on I have to remember to turn it off in traffic every time. Does the system really save petrol and is it harmful to the engine to constantly turn on and off. I was told starting the engine was the time of heavy fuel use and wear?