Fuel System:
* Fuel filter: A clogged fuel filter restricts fuel flow, leading to hesitation and bucking, especially under acceleration. This is a very common and relatively inexpensive fix.
* Fuel pump: A weak or failing fuel pump might not deliver enough fuel under demand. You might notice this more under acceleration.
* Fuel injectors: Clogged or failing fuel injectors can cause a misfire in one or more cylinders, leading to rough running and bucking.
* EGR valve: A sticking or malfunctioning Exhaust Gas Recirculation valve can disrupt the air/fuel mixture, especially during light throttle.
* Fuel pressure regulator: A faulty regulator could deliver incorrect fuel pressure.
Ignition System:
* Spark plugs and wires: Worn, fouled, or damaged spark plugs and wires can lead to misfires and poor combustion. This is another very common cause.
* Ignition coil: A failing ignition coil can result in weak or intermittent spark to one or more cylinders.
* Distributor cap and rotor (if applicable): Cracks or corrosion in the distributor cap and rotor can impede spark delivery. (The '95 might have distributor ignition, depending on the engine).
* Ignition module (or PCM): A failing ignition module (or the Powertrain Control Module/PCM) can cause erratic ignition timing or spark delivery. This is a more complex problem.
Air Intake System:
* Mass Airflow Sensor (MAF): A dirty or faulty MAF sensor provides inaccurate air flow readings to the PCM, leading to poor fuel mixture and running problems.
* Throttle Position Sensor (TPS): A malfunctioning TPS sends incorrect throttle position information to the PCM, affecting fuel delivery.
* Vacuum leaks: Leaks in the vacuum lines can disrupt the operation of various engine components, including the fuel system and EGR valve. Listen closely for hissing sounds near the engine bay.
* Air filter: While less likely to cause bucking under no load, a severely clogged air filter can restrict airflow enough to cause issues.
Other Possibilities:
* PCU (Power Control Unit)/PCM (Powertrain Control Module): A failing PCM can cause a wide range of problems. Diagnosing this requires specialized tools.
* Catalytic converter: While more likely to cause issues under load, a severely clogged catalytic converter could cause backpressure affecting the engine's breathing.
Troubleshooting Steps:
1. Start with the basics: Check the air filter, fuel filter, spark plugs, and wires. These are the easiest and cheapest things to check first.
2. Listen for unusual sounds: Hissing (vacuum leak), ticking (injector), knocking (internal engine issue).
3. Check engine codes: Use an OBD-II scanner to read any diagnostic trouble codes (DTCs) stored in the PCM. This can provide valuable clues.
4. Visual inspection: Look for any obvious signs of damage or wear to hoses, wires, or components.
If you're not comfortable working on your own vehicle, it's best to take it to a qualified mechanic for diagnosis and repair. They have the tools and experience to pinpoint the problem more efficiently. Providing the engine size (e.g., 5.0L, 5.8L) will help any mechanic diagnose the problem faster.
