Symptoms of a bad throttle position sensor

Written by william norman
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Symptoms of a bad throttle position sensor
Unsteady acceleration may indicate a throttle position sensor problem. (Image by Flickr.com, courtesy of Hamed Saber)

Modern vehicles feature sophisticated computer-controlled engine systems. These systems, however, can only perform as well as the data fed them by their electronic sensors. The throttle position sensor helps the engine set the correct fuel mixture for the vehicle from moment to moment, and if this sensor malfunctions, the car can experience a host of problems, such as stalling, rough idling and lacklustre engine performance.

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Description

A throttle position sensor works as a potentiometer, sending variable voltage signals to a car's main computer to let it know how far the throttle plates have opened. The engine then uses this data to calculate the proper mix of air to fuel the car's needs at that moment for optimal performance. The sensor feeds a low-level signal--typically less than one volt--to indicate a fully closed throttle, adding voltage gradually as the throttle opens and sending a full five volts when the throttle opens completely.

Acceleration Problems

A car that seems to hesitate or stumble during acceleration may have a faulty throttle position sensor. AA1Car.com explains if the sensor sends the wrong throttle position message to the engine, the engine will not add extra fuel to the mixture until the oxygen sensor feedback circuit steps in to correct the imbalance. This momentary miscommunication will cause the car to hesitate. Sometimes a sensor may develop one or more dead spots in its response, so as the potentiometer passes those spots, the car hesitates. Sensor wear often causes a dead spot just above its normal "idling" position.

Intermittent Problems

If your car idles unevenly or hesitates intermittently, regardless of acceleration, the throttle position sensor may simply have a loose connection. This loose connection sends out multiple signals, confusing the computer with indications that the throttle keeps opening and closing.

Poor Initial Performance

If your car engine seems to perform roughly from its first day on the road, the throttle position sensor may suffer from an incorrect initial setting. Throttle position sensor settings must conform to factory specifications precisely, and normally a new car has had its throttle position sensor adjusted to within 1/100 of a volt. A car that may seem like a "lemon" may in fact need only a tiny adjustment to the throttle position sensor setting to run perfectly.

Troubleshooting

A device called a multimeter can detect incorrect voltages issuing from the throttle position sensor. As described by the Electronics Club website, a multimeter typically includes an voltmeter, ohmmeter and other capabilities. Wells Manufacturing Company recommends attaching the meter to the sensor without the engine or ignition engaged. If you open the throttle slowly by hand, you should see a smooth rise or drop on the multimeter's voltage display. Testing all three terminals on the sensor can either isolate or eliminate the sensor as the cause of the throttle problem.

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