Hello guys, I have a 99 ford Mustang regular, V6 3.8L Engine. I'm 22 don't know too much about cars, but lately I've been getting really bad gas mileage, around 13 mpg. I'm used to getting about 20 ish. I can also smell a hint of gas when I start it and whilst driving sometimes. I took it to autozone, and some codes read up. It pretty much said that my mass air flow sensor something with my O2 sensors, the system was too lean, and I had some type of emissions or gas leak. I was wondering what would be the reason I'm getting such ty gas, and such bad idling/rough acceleration. I have never changed the air filter or cleaned the Mass air flow sensor or changed my O2 sensors. I was wondering if either of those would be the main reason for such gas mileage or is it the emissions leak?