I have an '01 S4 that recently went from getting 22mpg to 16.6mpg...and NO, its not because i am racing around town, in fact, i am driving like a grandma in hopes to get over 17mpg. I know this is a broad question, but what could be the culprit for this sudden decrease?? I filled the antifreeze (that was below the minimum line) like a week ago but it has not gone down since. That is the only thing that is out of the ordinary, everything is running like usual and i dont have a loss of power (although i haven't really tested it, remember, grandma driving...). I have APR's software but i have had it for around a year without any problems. Any feedback would be greatly appreciated!!!