On Thursday, April 11, 2019 at 11:36:58 AM UTC-10, Sheldon wrote:
>
> Mine too, that is ever since the lower grades contain ethonol...
> ethonol mkes engines run rougher and gives poorer MPG.

My guess is that the high octane gas also contain ethanol. It does lower your fuel mileage but the ethanol also suppressed engine knock which allowed me to use one grade lower of gasoline. I didn't notice my engines running rougher. Perhaps you had a potato stuck up your tailpipe.