* Throttle Position Sensor (TPS) Issues: The TPS is mounted on the throttle body and tells the ECU the throttle plate's position. If the TPS is faulty (e.g., stuck open, inaccurate readings), it might send incorrect signals to the ECU. The ECU, believing the throttle is open more than it actually is, will command the injectors to deliver more fuel, resulting in a rich mixture. This is a very common cause.
* Vacuum Leaks: A vacuum leak *after* the throttle body can affect the air/fuel ratio. The ECU relies on vacuum readings to determine the proper fuel mixture. A leak throws this off, often causing the ECU to compensate by adding more fuel to maintain a target air/fuel ratio. While not directly a throttle body issue, a leak near or around the throttle body can easily be mistaken for one.
* Throttle Body Position: While less common, a severely dirty or sticking throttle body might not close completely. This creates a constant air intake, leading the ECU to compensate by adding more fuel. This is more likely to cause a constant rich condition rather than intermittent issues.
In short, the throttle body itself doesn't "push" fuel; it controls airflow. A problem with the throttle body or its associated sensors leads the ECU to mistakenly command the injectors to deliver more fuel than needed. The root cause is almost always a sensor malfunction (TPS most often) or a vacuum leak, not a mechanical fault within the throttle body itself.
