Is it important to use mid-grade fuel on a foreign car such as an audi? What difference will it make?

Just follow the fuel recommendation in the manual or on a decal just inside the fuel cap cover. Using octane 91 when only 89 is required will not get you any better gas milage.





Be aware, turbo or supercharged engines do require 90 to 91 octane or higher becasue of the high combustion pressures inside the engine.





Also, differnet brand gas stations use different amounts of detergent in thier gasoline. That is how some stations try to save money. By using less or cheaper detergent in the fuel.