BMW 330i xDrive Car is getting worse gas mileage Inspection at your home or office.

Common reasons for this to happen:

• Dirty Oxygen Sensor: An oxygen sensor measures exactly how rich or lean the exhaust gases are when they leave the combustion chamber. The data is used by the vehicle computer to adjust the amount of fuel entering the engine. If the sensor is dirty or failing it can lead to a drop in miles per gallon. It can also lead to failed emission tests and a rough idle.

• Dirty Fuel Injectors: Fuel injectors spray fuel into the cylinders where it is mixed with air and ignited. Over time the fuel injector system can become clogged. This can lead to a drop in fuel efficiency as well as slow acceleration and the car not having enough power. If caught early, simply cleaning the injectors can solve the problem. As it progresses, the injectors may have to be replaced.

• Bad or Dirty Spark Plugs: Spark plugs ignite the fuel in the combustion chamber. If they are dirty or working incorrectly, it can cause the engine to misfire, leading to poor engine performance. This can lead to a lack of power as well as a big decline in fuel efficiency.

• Malfunctioning Mass Airflow Sensor: A mass airflow sensor detects the amount of air coming into the fuel injection system. It delivers that information to the vehicle's computer, which crunches the numbers and then delivers the proper amount of fuel to the air in the vehicle. A dirty airflow sensor will degrade fuel efficiently and lead to a rough idle and even stalling as the problem progresses.

• Misaligned Tires: Tires that are low or out of alignment can lead to a drop in fuel efficiency. Checking the tire pressure and have the alignment checked on regular basis can help prevent this problem.

• Defective Fuel Pump: Fuel delivery issues can drastically affect fuel efficiency. The fuel pump pulls fuel from the gas tank to the fuel injectors. The fuel pump can become clogged or malfunction. A bad fuel pump can lead to a rough running engine because it is not getting enough fuel. This will lead to a decline in gas mileage. If this issue is not addressed it will lead to a rough, idle, sputtering and stalling.

• Clogged Fuel Filter: A clogged fuel filter will also cause problems with gas mileage. The fuel filter screens out contaminants in the fuel, and over time it will become clogged. Fuel filters need to be replaced periodically.

• Stuck Brake Caliper: A stuck caliper on a disc brake or a stuck shoe on a drum brake can lead to a serious decline in gas mileage. In addition, any brake issue can make the vehicle dangerous to drive. If the decline in efficiency is accompanied by the vehicle pulling to one side, the brake system should be inspected immediately.