I just had a very interesting thing happen on my 97 I30. The battery condition indicator on this car has not been green since we bought the car over 2 years ago. About a week or so ago the battery finally died and I replaced it. Since the battery was replaced the car is running great! I check my milage every time I fill up and on the first tank full since the battery was replaced it was up almost 10%.
This makes a lot of sense since we have so many electronic sensors and controls on the engine! If I were you and were having weird performance and/or decreased milage problems I would check out the battery! Any one else run into this situation?
Be well!!!!