1. Idle Air Control (IAC) Valve: The IAC valve controls the amount of air that bypasses the throttle plate at idle. If it's dirty or malfunctioning, the engine may struggle to maintain a smooth idle and require you to press the gas pedal to keep it running.
2. Throttle Position Sensor (TPS): The TPS tells the engine control module (ECM) the position of the throttle. A faulty TPS can give incorrect readings, causing the ECM to send the wrong fuel and spark signals, leading to poor idle and starting problems.
3. Vacuum Leak: A vacuum leak can cause the engine to run lean, which can lead to a rough idle and starting issues. Check for cracks or loose connections in vacuum hoses and lines.
4. Fuel Pressure Issues: Low fuel pressure can also prevent the engine from starting properly. Make sure the fuel pump is functioning correctly and that there are no leaks in the fuel lines.
5. Spark Plugs and Wires: Worn spark plugs and wires can cause misfires, which can affect idle and starting. Check the condition of your spark plugs and wires and replace them if necessary.
6. Engine Sensors: Various other sensors can influence engine operation. Check the condition of your oxygen sensor, coolant temperature sensor, and mass airflow sensor.
Here's what you can do:
1. Check for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to check for any error codes stored in the ECM. This can provide valuable clues about potential problems.
2. Inspect the IAC Valve: Clean the IAC valve with a carburetor cleaner and ensure it moves freely.
3. Check the TPS: Use a multimeter to check the resistance of the TPS. If it's out of spec, replace it.
4. Inspect for Vacuum Leaks: Look for any cracked or loose vacuum hoses and lines.
5. Check Fuel Pressure: Use a fuel pressure gauge to test the fuel pressure.
6. Inspect Spark Plugs and Wires: Check the condition of your spark plugs and wires and replace them if necessary.
Important Notes:
* Safety First: Disconnect the battery before working on any electrical components.
* Professional Help: If you're not comfortable working on your car yourself, it's best to take it to a qualified mechanic.
By addressing these potential issues, you can hopefully get your 1994 Chevrolet G20 running smoothly again.
