Ignition System:
* Worn or faulty spark plugs/wires: Even new plugs can be faulty, and wires can develop cracks that only appear under high voltage loads (acceleration). Check for cracks or arcing.
* Distributor cap and rotor: Cracks or wear in the distributor cap or rotor can lead to poor spark distribution, especially under stress.
* Ignition coil: A weak coil might struggle to deliver sufficient voltage under high engine demands. It may test okay at idle but fail under load.
* Ignition module (or control unit): This component controls the ignition timing and spark. A failing module can cause intermittent issues.
* Crankshaft Position Sensor (CKP): If the sensor is faulty or dirty it may not send a proper signal to the ECU when under stress, resulting in misfires.
Fuel System:
* Fuel pump: While less likely if it's running at idle, a weak fuel pump might struggle to keep up with the increased demand for fuel during acceleration. Listen for a change in the pump's sound under acceleration.
* Fuel filter: A clogged fuel filter will restrict fuel flow, particularly under load, leading to lean conditions and misfires.
* Fuel injectors: A clogged or sticking injector could cause intermittent fuel delivery problems. This would require a fuel pressure test to confirm (often involves specialized equipment).
* Fuel pressure regulator: This component regulates the fuel pressure in the system. A faulty regulator could lead to inconsistent fuel pressure and misfires.
Other Possibilities:
* Vacuum leaks: A vacuum leak can disrupt the air/fuel mixture, leading to poor combustion and misfires, particularly noticeable under acceleration. Inspect all vacuum lines and connections carefully.
* Camshaft Position Sensor (CMP): Similar to the CKP, a faulty CMP sensor can cause timing issues resulting in misfires, especially under acceleration.
* Engine Temperature Sensor: An incorrect reading could lead to inappropriate fuel/air mixture adjustments.
Troubleshooting Steps:
1. Systematic approach: Check the simplest things first (plugs, wires, cap, rotor) before moving to more complex components.
2. Visual inspection: Carefully inspect all components for obvious signs of wear, damage, or corrosion.
3. Listen for unusual sounds: Pay close attention to any unusual sounds from the engine, particularly during acceleration (e.g., ticking, clicking, whining from the fuel pump).
4. Use a multimeter: Check the voltage output of the coil and sensors.
5. Fuel pressure test: If you suspect a fuel delivery problem, a fuel pressure test is essential.
Because this is an older car with potential for multiple aged components, it’s possible multiple small issues are compounding each other. A systematic approach and professional diagnosis may be required to pinpoint the exact cause. Ignoring a seemingly minor issue could lead to more serious damage.
