1. Fuel Delivery Problems (Beyond the Filter):
* Fuel Pump: A weak or failing fuel pump might deliver fuel at low pressure, enough to idle but insufficient for acceleration. Listen closely near the fuel tank for a humming sound when the ignition is turned on (but engine not running). A weak hum or no hum indicates a potential problem. Fuel pressure testing is crucial here.
* Clogged Fuel Injectors: Even with a new filter, injectors can become clogged with debris or varnish. They might spray insufficient fuel under load. Cleaning or replacing them is a possibility.
* Fuel Pressure Regulator: This regulates fuel pressure within the system. A faulty regulator can cause low or inconsistent pressure.
2. Ignition System Issues:
* Spark Plugs and Wires: While less likely given the engine runs, worn or faulty spark plugs or wires can drastically reduce performance under load. Check for cracks, corrosion, and proper gap on the plugs.
* Ignition Coil: A failing coil may not provide sufficient spark energy at higher RPMs.
* Distributor Cap and Rotor (if applicable): Older vehicles might have a distributor. Check for cracks, corrosion, or wear on the cap and rotor. (Less likely on a 1998, but worth checking if applicable to your specific engine).
* Crankshaft Position Sensor (CKP) or Cam Position Sensor (CMP): These sensors tell the computer the engine's position. A faulty sensor can lead to erratic performance or no acceleration.
3. Air Intake and Exhaust:
* Clogged Air Filter: While less likely given the problem description, a severely clogged filter can restrict airflow enough to affect acceleration.
* Exhaust Restriction: A severely clogged catalytic converter or muffler can restrict exhaust flow, affecting engine performance.
4. Throttle Body and Related Components:
* Dirty Throttle Body: A dirty throttle body can impede airflow. Cleaning it is a relatively easy fix.
* Throttle Position Sensor (TPS): This sensor tells the computer the throttle's position. A faulty TPS can cause poor performance. It needs testing with a multimeter.
* Mass Airflow Sensor (MAF): This sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor will cause incorrect fuel delivery.
5. Transmission Issues (Automatic Transmission):
* Torque Converter: If it's an automatic transmission, a failing torque converter could prevent power transfer during acceleration.
* Transmission Fluid: Low or contaminated transmission fluid can cause issues.
Troubleshooting Steps:
1. Check for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to read any stored trouble codes. This is the *first* step. Many auto parts stores will scan it for free.
2. Listen Carefully: Pay attention to any unusual noises from the engine or transmission.
3. Visual Inspection: Inspect all hoses, wires, and connections for damage.
4. Fuel Pressure Test: This is crucial to rule out fuel pump and regulator problems.
5. Professional Diagnosis: If you're not comfortable tackling these checks yourself, take it to a mechanic. The diagnostic time will be well worth the cost in the long run.
Remember safety first! Working on your vehicle can be dangerous. If you're not comfortable working on cars, have a qualified mechanic diagnose and repair the problem.
