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Not as far as I am aware. It was more as if the computer suddenly decided that the engine was run in and decided it could use less fuel. I had a similar experience on a new car a couple of years ago, but I can't remember which one it was (I change cars a lot)

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Had a similar thing happen in my mk5, just happened overnight. Better response and mpg.
Must be an engine management thing. Don't remember it being a particular milelage (1k, 1.5k or 2k), maybe it's set for km?