hi wonder if anyone can help had my sirion mot,d and serviced recently local garage and i,m now only getting 25 mpg previously i was getting around 40 the garage has checked gas and diagnostic with no problems there and there dosent appear to be any leaks the garage did say they changed the spark plugs to long life ones which cost a fortune they also suggested that running the car with air/con. may be the problem but I,d have noticed this pre service????? wits end