hey guys got a 1.4 16v had it for some time now its a 53reg and on 58,588 the problems with it is that its brunin alot of petrol i know its not the exhaust its had a new one fited not long ago cant see it blowin just wen im doin 30mph in fifth gear the mpg go to 102 then drop down to 20.2 then 18.6mpg and stands at 18.6mpg anyone know what makein this do this and brunin hell of lot of my petrol