low gas mileage
Decreases in fuel economy are caused by things like fuel control issues (fuel injector leaks (https://www.yourmechanic.com/services/fuel-injector-replacement), bad O2 (https://www.yourmechanic.com/services/oxygen-sensor-replacement) or other sensors), transmission problems (won't shift into high gear, slipping, torque convertor clutch fails to lock-up), misfires (ignition related), low...