They said Costco gas could be causing it because their premium gas is bad and that they combine unused gas from many tanks…blah blah blah. He advised me to run the car for 2 weeks with good gas from Chevron.
This is mostly true. No one fills premium at Costco. Everyone is a penny pincher
My X5 was running perfectly when one day on a long 200 mile drive I filled her up with premium gas from a shit hole gas station near I-76 NJ turnpike. Immediately I got sluggish acceleration and CEL and low power warning. Got it cleaned and DTML fuel pump replaced at a dealer.
Bad gas specially dodgy pumps with poor sales can screw up your high performance engines. Its ok for Toyotas and Kias.