* Low Fuel Pressure: The fuel pump might be weak, the fuel filter clogged, or there's a leak in the fuel lines reducing pressure at idle when the demand is low. When you add throttle, the pump works harder and temporarily overcomes the pressure issue.
* Idle Air Control (IAC) Valve: This valve regulates the amount of air entering the engine at idle. A dirty, malfunctioning, or stuck IAC valve can cause a lean idle condition (not enough fuel for the air), leading to stalling.
* Throttle Position Sensor (TPS): The TPS tells the computer the throttle position. A faulty TPS can send incorrect signals, causing the computer to provide the wrong fuel mixture at idle.
* Mass Airflow Sensor (MAF) Sensor (if equipped): Measures the amount of air entering the engine. A dirty or faulty MAF sensor will disrupt the air/fuel ratio, possibly causing stalling at idle.
* Vacuum Leaks: Leaks in the intake manifold or vacuum lines can disrupt the engine's air/fuel mixture, especially at idle when the vacuum is higher.
* Computer (ECM) Issues: While less likely, a problem with the engine control module itself could cause erratic fuel delivery. This is usually diagnosed last.
Troubleshooting Steps (in order of easiest to hardest):
1. Check Fuel Pressure: Use a fuel pressure gauge to measure the fuel pressure at the fuel rail. Compare this to the factory specification for your engine. Low pressure indicates a problem with the pump, filter, or lines.
2. Inspect Fuel Filter: Replace the fuel filter. It's a cheap and easy preventative measure, and a clogged filter is a common cause of fuel delivery issues.
3. Clean the IAC Valve: Remove the IAC valve and clean it thoroughly with carburetor cleaner (following the cleaner's instructions carefully). This often solves idle problems.
4. Check for Vacuum Leaks: Carefully inspect all vacuum lines and the intake manifold for cracks or loose connections. Use a vacuum gauge to check for leaks.
5. Check/Replace TPS: A faulty TPS can be tested with a multimeter, or you might need a scanner to check its output. Replacing is sometimes easier than testing.
6. Check/Clean MAF Sensor (if equipped): Carefully clean the MAF sensor with MAF sensor cleaner (NEVER use anything else). Replacing is necessary if cleaning doesn't help.
7. Diagnostic Scan: Use an OBD-II scanner to read trouble codes (DTCs) from the ECM. These codes can point directly to the problem.
Important Note: Before starting any work, disconnect the negative battery terminal to prevent accidental short circuits. If you're not comfortable working on your vehicle's fuel system or electrical components, consult a qualified mechanic. Improper repairs can lead to further damage or injury.
