Understanding the Symptoms:
* Starts but doesn't idle: This suggests an issue with fuel delivery or ignition that's only present when the engine is trying to idle.
* Fuel pump, injectors, plugs, and wires replaced: You've ruled out some common suspects, which is great.
Possible Causes:
1. Fuel Pressure Issues:
* Fuel pump relay: Even though you replaced the fuel pump, the relay that controls it could be faulty. Check for proper voltage at the relay's terminals when the ignition is on.
* Fuel pressure regulator: A faulty regulator could be releasing too much pressure, causing the engine to starve for fuel at idle.
* Clogged fuel filter: A clogged filter can restrict fuel flow, especially at low engine speeds.
* Leaking fuel lines: A leak in the fuel lines can cause a drop in pressure.
2. Ignition Issues:
* Faulty ignition module: The module controls the spark to the plugs. A faulty module can cause intermittent or weak spark, leading to poor idle.
* Faulty ignition coil: Similar to the module, a faulty coil can also result in weak spark.
* Bad spark plug connections: Ensure the connections are tight and that the spark plugs are the correct type for your engine.
3. Air Intake System Problems:
* Vacuum leak: A leak in the intake manifold or vacuum lines can cause the engine to draw in excess air, leading to a lean mixture that makes idling difficult.
* Dirty throttle body: A dirty throttle body can restrict airflow and hinder idling.
4. Engine Management System:
* Faulty sensor: Sensors like the oxygen sensor, mass airflow sensor, or throttle position sensor can provide incorrect readings to the engine control unit (ECU), leading to improper fuel and ignition adjustments.
* ECU fault: Although less common, the ECU itself could be malfunctioning, causing erratic fuel and ignition timing.
Troubleshooting Tips:
1. Check Fuel Pressure: Use a fuel pressure gauge to test the fuel pressure at the fuel rail with the engine running. Refer to your owner's manual or a reputable repair manual for the correct specifications.
2. Inspect Intake System: Look for visible cracks or leaks in the intake manifold, vacuum lines, and air intake hose.
3. Clean Throttle Body: Remove the throttle body and clean it thoroughly with throttle body cleaner.
4. Scan for Codes: Use an OBD-II scanner to check for any fault codes stored in the ECU. Codes can provide clues about the source of the problem.
5. Consider a Professional: If you're not comfortable with diagnosing and repairing these issues, it's best to seek professional assistance from a qualified mechanic.
Important Note:
* Always disconnect the battery before working on electrical components.
* Be cautious when working with fuel lines and systems to prevent fire hazards.
Good luck with your repair!
