Here's what you should do:
1. Get the Diagnostic Trouble Codes (DTCs): This is the most crucial step. You need to retrieve the codes stored in the car's computer. You can do this in a few ways:
* OBD-II Scanner: Buy a cheap OBD-II scanner from an auto parts store. Plug it into the OBD-II port (usually under the dashboard) and it will read the codes. Write down the codes exactly as they appear.
* Auto Parts Store: Most auto parts stores will scan your car for free. They can often give you a preliminary interpretation of the codes.
2. Interpret the DTCs: Once you have the codes, look them up online (many resources are available, just search for "OBD-II code [your code]"). This will give you a clue about the potential problem. Common causes of idle stutters and low acceleration in older vehicles include:
* Mass Airflow Sensor (MAF) Problems: A dirty or faulty MAF sensor can cause a lean fuel mixture, leading to rough idling and poor acceleration.
* Throttle Position Sensor (TPS) Issues: A failing TPS can give the computer incorrect information about the throttle position, resulting in erratic engine behavior.
* Ignition Coil Problems: A weak or failing ignition coil can cause misfires, leading to stuttering and poor acceleration. Even if you replaced spark plugs, a faulty coil won't let them fire properly.
* Crankshaft Position Sensor (CKP) Problems: This sensor tells the computer where the crankshaft is in its rotation. A faulty sensor can cause misfires and starting problems.
* EGR Valve Problems: The Exhaust Gas Recirculation valve can get clogged and cause rough idling and performance issues.
* Vacuum Leaks: A leak in the intake manifold or vacuum lines can disrupt the air/fuel mixture.
* Fuel Injectors: Clogged or malfunctioning fuel injectors can cause inconsistent fuel delivery.
3. Address the DTCs: Based on the codes and their likely causes, you can troubleshoot and repair the identified problem. Some repairs you might be able to do yourself (like cleaning the MAF sensor), while others will require more advanced tools or professional help.
4. Consider Other Possibilities (If DTCs Don't Point to a Clear Answer): If the codes don't provide a clear solution, consider the following:
* Fuel Pressure: Low fuel pressure could be the culprit, even if the fuel filter is new. A fuel pressure gauge is needed to check this.
* PCV Valve: A clogged Positive Crankcase Ventilation valve can lead to performance issues.
Important Note: Don't just start randomly replacing parts. Getting the diagnostic trouble codes is essential to avoid wasting money on unnecessary repairs. The check engine light is your guide – use it!
