Fuel Delivery Problems:
* Fuel pump: A weak or failing fuel pump can't deliver enough fuel to the engine under demand. This is more likely to be noticeable under acceleration.
* Fuel filter: A clogged fuel filter restricts fuel flow, leading to a lean condition. This is a relatively inexpensive and easy part to replace.
* Fuel injectors: Clogged or malfunctioning fuel injectors may not be spraying the correct amount of fuel into the combustion chamber. They can become clogged with debris or wear out over time.
* Fuel pressure regulator: A faulty regulator might not maintain the correct fuel pressure.
* Leaking fuel lines or connections: A leak in the fuel system reduces the amount of fuel reaching the engine.
Air Intake System Issues:
* Mass Air Flow (MAF) sensor: This sensor measures the amount of air entering the engine. A faulty MAF sensor can provide inaccurate readings, causing the computer to deliver less fuel than needed. This is a very common cause of lean conditions.
* Air leaks: Leaks in the intake manifold gaskets, vacuum lines, or other parts of the intake system allow unmetered air to enter the engine, throwing off the air/fuel mixture. This is often difficult to diagnose and requires careful inspection.
* Throttle Position Sensor (TPS): An inaccurate TPS reading can cause the computer to miscalculate the air/fuel mixture.
Other Potential Causes:
* Oxygen sensor (O2 sensor): While a faulty O2 sensor can cause lean conditions, it's more likely to cause a rich condition (too much fuel). However, a sensor failure *can* cause erratic behavior, possibly leading to a lean condition.
* Computer (PCM/ECM): In rare cases, a faulty engine control module (PCM or ECM) can cause incorrect fuel delivery. This is usually diagnosed after other more common issues are ruled out.
* EGR Valve: A malfunctioning EGR (Exhaust Gas Recirculation) valve can contribute to a lean condition, although this is less common.
* Vacuum Leaks: Small vacuum leaks can upset the carefully balanced air/fuel mixture and lead to running lean.
Troubleshooting Steps:
1. Check the OBD-II codes: A scan tool can retrieve diagnostic trouble codes (DTCs) stored in the car's computer. This is the first and most important step.
2. Inspect fuel pressure: A fuel pressure gauge can measure the fuel pressure to see if it's within specifications.
3. Check for vacuum leaks: Carefully inspect all vacuum lines and connections for leaks.
4. Inspect the MAF sensor and clean it (if possible): A dirty MAF sensor can give inaccurate readings.
5. Check fuel filter: This is a quick and easy check.
Important Note: Diagnosing fuel system problems requires some mechanical knowledge and the right tools. If you're not comfortable working on your car, it's best to take it to a qualified mechanic. Attempting repairs without proper knowledge can potentially cause further damage.
