Your Geo fuel injector depends on an array of sensors to let it do its job, which is supplying fuel in the correct oxygen/gasoline mixture to the car's engine. Primarily, the Geo fuel injectors rely on the main computer in the engine to send a signal (via voltage) to open up its valves and release the fuel. The computer controls how long the injector stays open or in some cases how quickly it opens and closes. The main computer is known as the Electronic Control Module, Power Control Module, Electronic Control Unit or Brain Box. The main computer receives its information, in turn, from an array of sensors. The Mass Air Flow Sensor measures airflow with heat; the main computer uses the MAF data to establish the volume levels of air in the combustion system. The Air Flow Meter has a built thermistor, which is an instrument that measures ambient air temperature. The Throttle Position Sensor measures the position of the throttle plate. The TPS tells the computer when the car is idling or when the driver is accelerating. The TPS also helps the computer determine if the airflow will permit the proper stoichiometric ratio. The Manifold Absolute Pressure Sensor is a combination of a vacuum diaphragm and a potentiometer. Poor oxygen sensors can cause the engine to run roughly because the fuel mixture will be too rich, or too lean. Take the time to diagnose whether your Geo fuel injectors are failing when you notice combustion problems, or whether the sensors are at fault.