* Faulty Throttle Position Sensor (TPS): This sensor tells the computer the throttle's position. A faulty TPS can send incorrect signals, leading the computer to inject excessive fuel. A malfunctioning TPS often results in poor idle, rough running, and increased fuel consumption.
* Vacuum Leaks: Leaks in the vacuum lines connected to the throttle body or other engine components can disrupt the air/fuel mixture. A lean mixture (too much air) can cause the computer to compensate by adding more fuel, resulting in higher than normal fuel consumption. Check all vacuum lines for cracks or loose connections.
* Faulty Idle Air Control (IAC) Valve: The IAC valve regulates air flow at idle. A malfunctioning IAC can cause the engine to idle too high or too low, and lead to excessive fuel use. A dirty IAC valve can also contribute to this.
* Fuel Pressure Regulator (FPR): If the FPR is malfunctioning, it might be delivering too much fuel pressure to the fuel injectors. This will lead to a rich fuel mixture and excessive fuel consumption.
* Mass Air Flow (MAF) Sensor (if equipped): The MAF sensor measures the amount of air entering the engine. A faulty MAF sensor can provide inaccurate readings, causing the computer to inject the wrong amount of fuel.
* Dirty or faulty throttle body: A dirty throttle body can cause the throttle plate to stick slightly open, resulting in a higher idle and increased fuel consumption. Buildup can also interfere with the TPS.
* Fuel injectors: Faulty or sticking fuel injectors can continuously inject fuel, even when not needed.
* Computer issue (PCM/ECM): While less common, a problem within the engine control module itself could cause incorrect fuel delivery calculations.
Troubleshooting steps:
1. Check for vacuum leaks: Visually inspect all vacuum lines and connections for cracks or loose fittings. Use a vacuum gauge if necessary.
2. Clean the throttle body: Remove the throttle body and clean it thoroughly with throttle body cleaner. Pay attention to the throttle plate and ensure it moves freely.
3. Check the TPS voltage: Use a multimeter to check the voltage output of the TPS. This requires consulting a wiring diagram for your specific vehicle.
4. Check the IAC valve: Ensure the IAC valve is clean and operates freely.
5. Check fuel pressure: A fuel pressure gauge is needed to measure fuel pressure. This should be done with the engine running.
6. Have the MAF sensor (if equipped) checked or replaced: This often requires a professional scan tool to diagnose correctly.
7. Professional Diagnosis: If you're not comfortable performing these checks, it's best to take your vehicle to a qualified mechanic for a proper diagnosis. They have the tools and expertise to pinpoint the problem.
Remember safety first! Always disconnect the negative battery terminal before working on any electrical components. Be cautious when working with fuel systems, as fuel is flammable.
