Would everyone be willing to spend $250-$400 on DHP or HPT just to tune their cars for a 5% increase in gas mileage?
Not everyone can get the same effect, but is it really that hard to believe that one could get an increase in MPG by adjusting for a LTFT that reads excessively rich? You would think that by leaning it out, you would actually be putting less fuel into the engine?
It may not be 5 mpg for every person that does it, but it can be substantial for some who aren't exactly running "up to snuff" and need a tune in order for it to be perfect.
