Signs & Symptoms of a Bad Throttle Position Sensor on a Mazda MX-3


The Mazda MX-3 was a two-door coupe produced by the Japanese car maker from 1991 to 1998. The vehicle uses a multipoint fuel injection system that requires a throttle position sensor. The MX-3 can experience engine and fuel problems when this component malfunctions or fails. These issues can escalate into more serious engine problems if they are not addressed quickly.

Hesitation and Engine Stumble

  • A bad throttle position sensor in a Mazda MX-3 will cause the vehicle to hesitate or stumble during acceleration, according to automotive repair website AA1Car. The throttle position sensor sends the wrong information to the vehicle's onboard computer, which regulates the air-to-fuel mixture flowing through the MX-3's multipoint fuel injection system. The increased air impedes combustion within the engine, resulting in a lack of power during acceleration.

Unstable Idle

  • If the Mazda's throttle position sensor is worn or loosened from its mounting it may cause unstable idling and difficulty maintaining speed. A driver will experience this as an intermittent drop in revs per minute, which can lead to engine shuddering and stalling out. The fluctuating signal causes the Mazda's onboard computer to believe the throttle is opening and closing, which leads to an inability to determine the position of the throttle. This condition may disappear once the vehicle is driving and suddenly reappear once it returns to an idle position.

Impaired Fuel Economy

  • A bad throttle position sensor can cause the MX-3's computer to believe the throttle is wide open all the time. This results in a rich fuel mixture, meaning too much fuel and not enough air is entering the engine. A driver will notice this symptom as diminished fuel economy. The vehicle's "check engine" light also may illuminate as a wide open throttle sometimes generates a fault code with the computer, according to the AA1Car website.

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