Fuel System:
* Fuel filter: A clogged fuel filter restricts fuel flow, leading to sputtering, especially under acceleration when the engine demands more fuel. This is one of the easiest and cheapest things to check/replace first.
* Fuel pump: A weak or failing fuel pump can't deliver enough fuel at higher engine speeds. You might hear a whining noise from the fuel pump if it's failing.
* Fuel injectors: Clogged or failing fuel injectors can cause inconsistent fuel delivery, leading to sputtering. This requires more specialized tools and knowledge to diagnose.
* Fuel pressure regulator: A faulty regulator might not maintain the correct fuel pressure, causing inconsistent fuel delivery.
* EGR Valve (Exhaust Gas Recirculation): A sticking or malfunctioning EGR valve can lean out the fuel mixture, causing sputtering.
Ignition System:
* Spark plugs and wires: Worn, fouled, or damaged spark plugs and wires can prevent consistent ignition, resulting in sputtering. These are relatively inexpensive and easy to replace.
* Distributor cap and rotor (if applicable): Cracks or corrosion in the distributor cap and rotor can disrupt the spark delivery.
* Ignition coil: A failing ignition coil won't provide enough voltage to the spark plugs, leading to misfires and sputtering.
* Ignition control module (ICM): This component controls the ignition timing and spark delivery. A faulty ICM can cause various ignition problems.
Other Possibilities:
* Mass airflow sensor (MAF): A faulty MAF sensor provides incorrect air/fuel mixture readings to the engine control unit (ECU), leading to poor performance.
* Throttle position sensor (TPS): A faulty TPS provides inaccurate information about throttle position, affecting fuel delivery.
* Computer (ECU): While less likely, a faulty ECU can cause a variety of problems, including sputtering.
Troubleshooting Steps:
1. Check the basics: Start with the easiest and cheapest fixes: Inspect the spark plugs and wires. Replace the fuel filter. Check for any loose vacuum lines.
2. Listen for unusual noises: Pay attention to any unusual sounds coming from the engine, particularly whining from the fuel pump.
3. Read trouble codes (if equipped): Many 1991 vehicles have a diagnostic port that can provide trouble codes indicating potential problems. You might need a code reader.
4. Professional diagnosis: If you're not comfortable working on your car yourself, take it to a qualified mechanic for diagnosis and repair. They have the tools and expertise to pinpoint the problem accurately.
Remember to always follow safety precautions when working on your vehicle. Disconnecting the battery negative terminal is a good idea before starting any work. The information above is for guidance only, and a proper diagnosis requires a thorough inspection.
