I did 91 for the first tank just to test the mileage, but also noticed in the maintenance manual that if you don't use top-tier detergent gasoline that they recommend a fuel additive every oil change. Of course the dealer will gladly do this for a cost or you could buy the bottle yourself. Not sure if this is a new thing or a carryover from Sedona or other Kia's though?
Well, considering this is a dual injected engine, top tier and the occasional additive would be wise. The direct injectors will do most of the fueling leaving the port injectors slightly more prone to deposits. Detergents don't do diddly for most direct injectors but can clean those lower pressure port injectors. I spoke with my salesperson and they recommended Mid Grade fuel. We almost always fuel at Costco where its 85 or 91. Maybe we'll just do the 91.
Agree an additive wouldn't hurt, but the port injectors should keep the intake valves much cleaner and hopefully avoid the need for expensive walnut-washing and other techniques needed on direct-injected engines. Here's a technical article: Dual Port and Direct-Injection Technology: What You Need to Know About the Next Generation of Engine Design
