hes correct. The reason your car may have run bad on certain gas is the viscosity of the fuel. For example say you bought gas in 80 degree weather at 5,000 ft above sea level. If you drove into a colder/warmer climate or higher/lower altitude your car won't noticed the change right away and it will cause it to run worse. It could take a few days or a few hours for the PCM to notice this change.