I have a 2007 Pontiac G6 GT 3.5 liter V6. One day I drove it and the check Engine light came on and a message came up on the display "Reduced Engine Power". The car started to run very badly. I parked it, looked under the hood saw no signs of anything wrong, disconnected the battery to reset the computer and the car ran fine!!! It happen again two days later!!! what would cause the car to do this????