machan there are no experts here,they live in belief that they are,u could be mislead, becareful, its not a defect on your EFI,your car just witnessed xtra premium,so since u are not going to complete pumping that,and sticking to your 90oct,u should get your desired value,and try changing your gears by 1600-1800RPM,this will help too,thats only if u want machan.
hope it comes in handy