94 Aerostar fuel/air mix and timing

A friend found his aerostar had the fuel/air ratio and timing programming settings significantly off from the factory. After he reset back to optimum he got a huge jump in MPG (+8 MPG, 32 hwy) ) and performance. No problems with passing emissions. I am looking at a Ranger of the same era/computer. Is this a common problem with their computers or is it an EPA thing?