Mixing diesel with petrol. Not a good idea, and especially not when you've just filled up in Chamonix and are about to go into the Mont Blanc tunnel. On the bright side it was only €0.55 worth before I noticed. What an idiot and I felt it too. Anyway I reckoned the mix would have been180 parts diesel to 1 part petrol but i drove it up and down the nearest bit of road for 20 klm anyway before comitting to going underground for 11 klms. All's well I'm glad to say.