right octane fuel use
 

I have purchased Audi Q7 and fear that the wrong octane fuel may have been put in the car. woulf this cause intermittent juddering during acceleration.
Can i get a fuel additive to get me through thei tank of fuel

Did you purchase a new car? If so, it is under warranty and any question of the engine shuddering should be taken up under warranty with service.

If it is a used car, was it a private sale? Or does it have a warranty?

You might specify what year and engine type the car has. If it is a flexfuel engine, it can eat almost anything and should still run smoothly. If the car came with manuals, READ THEM to find out what fuels are acceptable. Additives can only do so much and should make no real difference versus just burning up the fuel that is in it and adding new. Of course with even the best fuel, if there is water in the fuel or other contaminants, it may require more effort to clean out the fuel system.

But your options depend on what your car is (New? Private seller? Warranty?) and you don't tell us that.

Modern engines will automatically adjust for engine knock for different grades of fuel. So, there is no issue if for example it was filled with regular grade instead of premium, except you may notice a slight difference in performance. That said, you should try and use a premium grade Top Tier fuel in the future. Tests have been proven that Top Tier fuels are beneficial. (While DI engine valve carbon deposits won't benefit due to where the fuel is injected into the cylinders, Top Tier detergents will help to maintain the rest of the fuel paths).

Licensed Brands | Top Tier Gas