Fuel System:
* Fuel pump: A weak fuel pump might deliver insufficient fuel, especially under acceleration. This is a common cause of stalling. Listen for a whirring sound from the fuel pump when you turn the ignition key (before cranking). A weak or failing pump may be quieter or make a different sound.
* Fuel filter: A clogged fuel filter restricts fuel flow, leading to similar symptoms. It's cheap and easy to replace; do this even if you've recently changed it.
* Fuel injectors: Clogged or faulty fuel injectors can cause a rough idle and poor acceleration. This requires more specialized testing. A fuel injector cleaner might help temporarily, but a proper diagnosis and possibly replacement might be necessary.
* Throttle Position Sensor (TPS): This sensor tells the computer the throttle's position. A faulty TPS can cause erratic idling and poor acceleration. It's relatively inexpensive and easy to replace.
* Mass Airflow Sensor (MAF): This sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor can cause a rich or lean fuel mixture leading to poor running. Cleaning it is a worthwhile first step.
* Fuel pressure regulator: This regulates the fuel pressure in the system. A faulty regulator can cause low or fluctuating fuel pressure.
Ignition System (Beyond the Coil):
* Distributor cap and rotor: Even with new wires and plugs, these components can still be worn or cracked, causing misfires. Inspect them for cracks, corrosion, or wear.
* Ignition control module (ICM): This module controls the ignition system. A failing ICM can cause intermittent misfires and stalling.
* Crankshaft Position Sensor (CKP): This sensor tells the computer where the crankshaft is in its rotation. A faulty CKP can lead to a variety of problems, including rough idle and stalling.
Other Possibilities:
* Vacuum leaks: Small vacuum leaks can disrupt the engine's air/fuel mixture, causing rough idling and poor performance. Inspect all vacuum hoses for cracks or leaks.
* EGR valve: The Exhaust Gas Recirculation valve can stick or malfunction, affecting the engine's mixture and causing rough running.
* PCV valve: A clogged PCV valve can cause excessive crankcase pressure, leading to various problems.
Troubleshooting Steps:
1. Check for trouble codes: Use a scan tool (even a cheap OBD-I scanner will work) to check for any stored diagnostic trouble codes (DTCs). These codes can point to the specific problem area.
2. Inspect the vacuum lines: Look for cracks, loose connections, or broken lines. Spray a small amount of carburetor cleaner around vacuum connections while the engine is running. A change in idle speed indicates a vacuum leak at that point.
3. Check fuel pressure: If possible, measure fuel pressure to ensure it's within the specification.
4. Clean the MAF sensor: Use MAF sensor cleaner (available at auto parts stores). Follow the instructions carefully.
5. Inspect the distributor cap and rotor: Check for cracks, corrosion, or wear. Replace if necessary.
6. Test the TPS and CKP sensors: These sensors can be tested with a multimeter, but often require a specific procedure depending on your vehicle. A professional mechanic can do this reliably.
It's likely that addressing one or more of these issues will resolve the problem. If you're not comfortable working on your car yourself, take it to a qualified mechanic for diagnosis and repair. Providing them with the information that you've already replaced the wires, plugs, and potentially improved the coil will save time and money on the diagnosis.
