Ignition System:
* Spark Plugs: Worn, fouled, or improperly gapped spark plugs are a very common cause of rough running. They're relatively inexpensive and easy to check/replace.
* Wires: Cracked or damaged spark plug wires can prevent a consistent spark reaching the plugs. Look for cracks or signs of wear.
* Ignition Coil(s): The coil(s) provide the high voltage to the spark plugs. A failing coil can cause misfires in one or more cylinders. This is more likely to cause a rough idle or misfire at specific RPMs.
* Distributor Cap and Rotor (if applicable): Older vehicles may have a distributor. A worn or damaged distributor cap and rotor can interrupt the spark delivery. (The 1997 Concorde likely uses coil-on-plug, so this is less likely, but worth considering if it hasn't been checked recently.)
* Crankshaft Position Sensor (CKP): This sensor tells the engine's computer where the crankshaft is in its rotation, crucial for timing the spark. A faulty CKP sensor can cause a variety of issues, including rough running.
Fuel System:
* Fuel Injectors: Clogged or malfunctioning fuel injectors can deliver an inconsistent fuel spray, leading to misfires and rough running.
* Fuel Filter: A clogged fuel filter restricts fuel flow, starving the engine of fuel and causing rough running, especially under load.
* Fuel Pump: A weak or failing fuel pump can't deliver enough fuel pressure, leading to similar symptoms.
Air Intake System:
* Mass Airflow Sensor (MAF): This sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor can cause inaccurate fuel delivery, resulting in a rough idle or running.
* Air Filter: A severely clogged air filter restricts airflow and can lean out the air/fuel mixture.
Other Potential Causes:
* Vacuum Leaks: Leaks in the vacuum system can disrupt the engine's timing and fuel mixture.
* PCV Valve: A plugged PCV (Positive Crankcase Ventilation) valve can cause excessive crankcase pressure, affecting engine performance.
* Engine Mounts: Worn engine mounts can cause the engine to vibrate excessively, leading to a rougher feel. This wouldn't necessarily be a *running* problem, but rather a shaking/vibrating problem.
* Oxygen Sensor: Although less likely to directly cause a rough idle, a faulty O2 sensor can affect fuel mixture over time and contribute to poor performance.
Troubleshooting Steps:
1. Check for error codes: Use an OBD-II scanner to read any diagnostic trouble codes (DTCs) stored in the engine's computer. This can pinpoint the problem area.
2. Inspect visually: Check for obvious signs of damage, leaks, or wear in the ignition system, air intake, and vacuum lines.
3. Start with the basics: Replace spark plugs and wires. This is the cheapest and easiest thing to try first, and often solves the problem.
4. Systematic approach: If the problem persists, work your way through the other possibilities, checking components one by one based on likelihood and cost-effectiveness.
Remember, a proper diagnosis may require a mechanic with specialized tools and experience, especially if the problem isn't easily identified. Don't attempt repairs beyond your skill level.
