I stopped using Cosco for fuel after about a year when my vehicle engine light started turning on. Code indicated loose cap, but it never was loose. Switched back to mainly Chevron and problem went away. Shortly later, the O2 sensors before the converter failed. I believe it was from the Costco fuel.
I always use premium to save on injector maintenance/replacement. I never had any injector problems. Individuals I know that use only regular fuel recommended for their vehicles usually end up with injector issues. Premium is always $0.20 higher than regular at any price. When prices go up, premium tends to be better value.
