BMW 318i Throttle Position Sensor Replacement Cost

By reading the position of the throttle, the sensor indicates how much air is being let into the engine. The car's computer uses this reading to send the correct amount of fuel to the engine, where it mixes with the air and is burned. 

When a throttle position sensor is defective, the vehicle may hesitate, misfire, or jerk on acceleration, shift poorly, and display uneven power characteristics.

The Check Engine Light may illuminate with a fault code set for one or more throttle position sensors.

When the throttle position sensor fails, the engine's computer tends to overcompensate with fuel, leading black exhaust coming from the tailpipe. There is a strong possibility of engine misfires, and the check engine light will come on. Throttle position sensors can also develop "dead spots," or certain places along the throttle curve where it doesn't get a reading. When this happens, the above symptoms can occur but then stop when you further press or let off the gas pedal.

When the throttle body position sensor fails, the vehicle may not start, or may start and then stall. Even if the car keeps running but idles roughly, it's best to get it repaired right away to avoid damaging other, more expensive parts.

Throttle position sensors failure is fairly common. The average lifespan of a throttle position sensor is just over 80,000 miles. There is no maintenance for a throttle position sensor — it simply needs to be replaced after it stops working correctly.

The technician will use a scanning tool to check for codes pointing to problems with the throttle position sensor. This also allows the technician to see operating conditions in real time. The technician will also check whether the sensor is adjusted properly in relation to the throttle plate.

A throttle position sensor code isn't always triggered by a defective sensor. It can be triggered by a defective crankshaft position sensor, MAP sensor, mass air flow sensor, ignition problem or defective PCM.

The battery must be disconnected, and other parts, such as an engine cover or strut brace, may need to be removed. The throttle position sensor is located opposite the spring for the throttle cable, and can be removed with a connector and a couple of screws. The sensor can be pulled out and tested, and the new sensor installed in its place.