Ignition System:
* Spark Plugs and Wires: Worn, fouled, or damaged spark plugs and wires are a very common cause of rough running. They prevent a consistent spark, leading to misfires.
* Ignition Coil(s): A failing ignition coil can't supply sufficient voltage to the spark plugs, causing misfires in one or more cylinders.
* Distributor Cap and Rotor (if applicable): Older Cadillacs might have distributors. Cracks or wear in the cap and rotor can disrupt the spark delivery.
* Ignition Control Module (ICM): This module controls the ignition timing and can fail, leading to rough running.
Fuel System:
* Fuel Injectors: Clogged or leaking fuel injectors can deliver inconsistent fuel to the cylinders.
* Fuel Filter: A clogged fuel filter restricts fuel flow, leading to a lack of power and rough running.
* Fuel Pump: A weak or failing fuel pump may not supply enough fuel pressure.
Engine Management System:
* Mass Airflow Sensor (MAF): A faulty MAF sensor provides inaccurate air flow readings to the engine computer, leading to poor fuel mixture and rough running.
* Throttle Position Sensor (TPS): A malfunctioning TPS provides incorrect throttle position data to the computer, affecting the fuel/air mixture.
* Oxygen Sensor(s): Faulty oxygen sensors provide inaccurate readings of exhaust oxygen levels, leading to improper fuel mixture.
* Engine Computer (PCM/ECM): Although less common, a failing engine control module can cause a variety of problems, including rough running.
Other Possibilities:
* Vacuum Leaks: Leaks in the vacuum system can disrupt the engine's timing and fuel delivery.
* PCV Valve: A faulty positive crankcase ventilation valve can cause excessive pressure buildup in the crankcase, affecting engine performance.
* Compression Issues: Low compression in one or more cylinders can cause a rough idle and poor performance. This could indicate worn piston rings, valve problems, or a blown head gasket.
Troubleshooting Steps:
1. Check Engine Light: If the check engine light is on, get the diagnostic trouble codes (DTCs) read using an OBD-II scanner. This will give you a starting point.
2. Listen to the Engine: Pay attention to any unusual sounds like knocking, ticking, or hissing.
3. Visual Inspection: Look for any obvious signs of damage, leaks, or loose connections.
4. Start with the basics: Replacing spark plugs and wires is often a relatively inexpensive first step and can resolve the issue in many cases.
Important Note: Without a proper diagnosis, replacing parts randomly can be expensive and may not solve the problem. It's best to take your 1997 Cadillac to a qualified mechanic for diagnosis and repair. They have the tools and expertise to pinpoint the exact cause of the rough running.
