My audi a4 does not want to start sometimes and I have no idea whats the problem. Sometimes it fires right up and others it takes a while. Sometimes it seems like the car is on but it immediately dies. It usually happens twice and the third time it always starts. Any ideas on whats happening? I'm also getting odd gas mileage. It says im getting 20 mpg but im about halfway through a tank of gas and only drove the car 4 days! My commutes are about 20 miles a day but it seems like somethings wrong. Please help

 

Crank position sensor. Is like 90 bucks. This link will help you.

 

thanks. the car is under warranty so it better be fixed. I now have to fix my window because it sides down and wont go back up.