[SOLVED] AKI Solved

Google is your friend...

"The AKI (anti-knock index -- also known as "octane rating") of the fuel is an average of two different methods of computing the fuel's ability to resist engine knock. Regular unleaded gas in the U.S. has an anti-knock index of 87, while mid-grade is usually 89, and premium typically is 91 - 93. The higher the number, the more anti-knock protection the fuel offers. "

I read the 89 AKI thing right after I put in 85 octane. How much is the 85 going to mess up my car? Was there any practical way I could have remedied my mistake once the gas was in there?

For one tank it won't hurt. But don't make a habit out of it. The BMW is designed for 89 octane, so that's what you should be putting into it.

Shouldn't hurt it but you could run in a few gallons of premium when you have room in the tank.

AKI = Anti-Knock Index. It is the US way of stating Octane requirements. There are two methods of measuring the octane of fuel, the motor method and the research method. Rather than pick one, the US requires that gasoline retailers post the average of the two numbers - (RON + MON)/2.

See:

Ed White