Im pretty sure somethings not right here..current spec on my glanza is: CT9B Turbo Standard Manifold Front Mount Intercooler Decat 2.5 Jperformance catback I know there was a slight leak from the decat which i believe i have solved. Considering replacing all the gaskets as i believe there might be a slight leak of exhaust gas somewhere(would this effect mpg). The car also idles at around 1,000rpm and my tracking is slightly out which i believe may be adding to the problem? Last option is lambda needs replacing after changing cat for decat?? can't remember my mpg before the decat. I wouldn't say the car runs noticeably rich. Should add that this is on Tesco Vpower at £132.9 a litre, generally runs around town, taking it steady the majority of the time.