Fuel System:
* Clogged Fuel Filter: A dirty fuel filter restricts fuel flow to the engine. This is a relatively easy and inexpensive fix.
* Fuel Pump: A failing fuel pump may not deliver enough fuel pressure to keep the engine running consistently. You might hear a buzzing sound from the fuel pump when you turn the key to the "on" position, but it might be weak or intermittent.
* Low Fuel Pressure: Problems with the fuel pump, fuel pressure regulator, or fuel injectors can cause low fuel pressure. A mechanic will need a fuel pressure gauge to diagnose this.
* Fuel Injectors: Clogged or faulty fuel injectors can prevent sufficient fuel from reaching the engine's cylinders.
* Fuel Delivery Lines: Cracks or leaks in the fuel lines can cause fuel starvation.
Ignition System:
* Crankshaft Position Sensor (CKP Sensor): This sensor tells the computer the position of the crankshaft. A faulty sensor prevents proper timing and can cause stalling.
* Camshaft Position Sensor (CMP Sensor): Similar to the CKP sensor, but for the camshaft. A bad sensor can lead to erratic engine operation and stalling.
* Ignition Coil: A failing ignition coil might not deliver enough spark to one or more cylinders.
* Spark Plugs and Wires: Worn or damaged spark plugs or wires can hinder ignition.
* Distributor (if applicable): Though less common in later model years, some 2004 Malibus might still have a distributor. Issues with the distributor cap, rotor, or internal components can disrupt spark delivery.
Air Intake System:
* Mass Airflow Sensor (MAF Sensor): This sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor can lead to a poor air-fuel mixture, causing stalling.
* Vacuum Leaks: Leaks in the vacuum lines can disrupt the engine's air-fuel mixture.
* Throttle Position Sensor (TPS): The TPS tells the computer the throttle's position. A faulty TPS can cause erratic idle and stalling.
Other Potential Issues:
* Computer (PCM) Problems: In some cases, a malfunctioning engine control module (PCM) can cause various problems, including stalling. This is usually a last resort diagnosis.
* Idle Air Control (IAC) Valve: This valve regulates airflow at idle. A dirty or faulty IAC valve can lead to stalling.
Troubleshooting Steps:
1. Check the obvious: Ensure you have enough fuel.
2. Listen for unusual noises: Any unusual sounds from the engine bay (clicking, buzzing, whirring) can provide clues.
3. Check engine codes: Use an OBD-II scanner to read any diagnostic trouble codes (DTCs) stored in the car's computer. These codes can point you toward the problem.
4. Inspect visually: Look for any obvious signs of damage, leaks, or loose connections.
Recommendation: Unless you're comfortable working on cars, it's best to take your 2004 Chevy Malibu to a qualified mechanic for diagnosis and repair. Trying to troubleshoot these issues without the proper tools and knowledge could lead to further damage or injury. The codes from the OBD-II scan will significantly help the mechanic pinpoint the issue.
