firstly ill say im NOT complaining about the mpg or anything like that,but i genuinely believe that my car is using a lot of fuel.it has been sitting around for about 2 years and has only covered 600 miles in that time.it idles a bit high and the revs sometimes dip and rise when it is ticking over.there are no leaks and i am not using it hard.is there a sensor or injector that can fail causing it to burn more fuel?the tailpipe is no more black than normal but it does smell a bit rich!any ideas?