* IAC (Idle Air Control) Valve: This valve regulates air flow at idle. A dirty or malfunctioning IAC valve is a very common cause of rough idle and stalling. Cleaning it (with carb cleaner, carefully) is often a cheap and easy first step. Replacement is inexpensive if cleaning doesn't work.
* MAF (Mass Airflow) Sensor: This sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor can provide inaccurate readings, leading to a poor air/fuel mixture and rough running. Cleaning it (with MAF sensor cleaner – *never* carb cleaner) is worth trying, but replacement might be necessary.
* Throttle Position Sensor (TPS): This sensor tells the computer the throttle's position. A faulty TPS can cause erratic idle and stalling. It's relatively inexpensive to replace.
* PCV (Positive Crankcase Ventilation) Valve: A clogged PCV valve can cause excessive crankcase pressure, leading to various engine problems, including rough idle and stalling. Replacing it is cheap and easy.
* Fuel System Issues:
* Fuel Filter: A clogged fuel filter restricts fuel flow, causing rough running and stalling. Replacing this is relatively inexpensive.
* Fuel Pump: A failing fuel pump may not deliver enough fuel pressure, leading to similar symptoms. This is more expensive to replace.
* Fuel Pressure Regulator: This regulates fuel pressure. A faulty regulator can cause inconsistent fuel delivery.
* Ignition System:
* Spark Plugs & Wires: Worn or fouled spark plugs and worn ignition wires can cause misfires, leading to rough idle and stalling. Replacing these is relatively inexpensive.
* Distributor Cap and Rotor (if applicable): These components (if your engine has a distributor) can degrade over time, causing ignition problems. Replacement is inexpensive.
* Ignition Coil: A failing ignition coil can cause misfires and stalling.
* Vacuum Leaks: Leaks in the vacuum system can disrupt the engine's air/fuel mixture, leading to a rough idle and stalling. These can be difficult to find.
* Engine Sensors (various): Many other sensors (e.g., coolant temperature sensor, oxygen sensor) can contribute to a rough idle if faulty. Diagnosing these usually requires a scan tool.
Troubleshooting Steps:
1. Check for trouble codes: Use an OBD-II scanner to read any diagnostic trouble codes (DTCs) stored in the car's computer. This can pinpoint the problem area.
2. Start with the easy and cheap fixes: Clean the IAC valve and MAF sensor. Check and replace the PCV valve and fuel filter. Inspect spark plugs and wires for wear.
3. Listen carefully: Does the rough idle change with the engine's temperature? Does it get worse when turning on accessories (like the AC)? These clues can help narrow down the possibilities.
4. Professional diagnosis: If you can't identify the problem after trying the above steps, take your Malibu to a qualified mechanic for diagnosis. They have the tools and expertise to accurately diagnose the issue.
Remember safety first! Work on the car in a well-ventilated area, and disconnect the negative battery terminal before working on any electrical components.
