Ed, the most likely explanation for your situation is that something was causing a problem and now it's not. Probably a partially plugged injector which has cleared itself. Probably doesn't have much to do with the gas. But, if you want to do some research, go back to the gas you were using before and see if the problem comes back, (doubt that it will).

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Jeff L
1987 300e
1989 300e
1987 BMW 325