When i choose Instant Fuel Usage on my dashboard readout it goes fron 25mpg up to 99mpg and back again. It is all over the place. Is it faulty, not fit for purpose or am i not using it right. Thanx. :)

Nothing wrong with it, its giving you "instant" mpg :)

when you take your foot off the gas off you get 99mpg because you are not using any fuel, when you accelerate you get 25mpg because your are using alot of fuel

Sorry....i meant to say i have a Focus 1.6 Zetec petrol 2009. :)

what I love about the instant reading is that you only tend to look at it when its safe to do so, its a subconscious thing. that means that the chances are your instant readings will always be higher than normal because your literally taking your foot off the gas to concentrate on it. its completely useless in towns and only really makes some sense on longer runs doing a consistent speed

Speak for yourself Darren... I've managed to get mine into the teens on several occasions...

Honestly though, its not even good for long runs imo, it's too slow to react then changes so much when it does so you can't alter throttle using it as a guide. Ignore it and just use the average one imo! :)