Fuel System:
* Fuel Pump: A failing fuel pump might not provide enough pressure when the engine is under low load (like when slowing down). This is more likely if the stalling only happens when slowing down significantly, not just idling.
* Fuel Filter: A clogged fuel filter restricts fuel flow, leading to similar symptoms as a failing fuel pump. This is a relatively inexpensive part to replace and should be checked early.
* Dirty Injectors: Clogged or malfunctioning fuel injectors can prevent sufficient fuel delivery, particularly under lower engine demands.
* Vacuum Leaks: Leaks in the vacuum lines connected to the fuel system can disrupt fuel pressure regulation, causing stalling.
Ignition System:
* Distributor Cap and Rotor (if applicable): Cracks or corrosion in these components can interrupt the spark, leading to stalling, especially under stress like slowing down. This is more common in older Cougars with distributors.
* Ignition Coil: A failing coil may not provide sufficient spark under load, resulting in misfires and stalling.
* Spark Plugs and Wires: Worn or damaged spark plugs or wires can cause misfires and inconsistent ignition, leading to stalling.
Idle Control:
* Idle Air Control (IAC) Valve: This valve regulates airflow at idle. A dirty or malfunctioning IAC valve can cause the engine to stall when slowing down because it can't maintain a consistent idle.
* Throttle Position Sensor (TPS): This sensor tells the computer the position of the throttle. A faulty TPS can provide inaccurate readings, leading to improper fuel delivery and stalling, especially during transitions like slowing down.
* Mass Airflow Sensor (MAF) Sensor: This sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor can give inaccurate readings, leading to poor fuel mixture and stalling.
Other Possibilities:
* Transmission Issues (Automatic): In automatic transmission vehicles, problems with the transmission itself, torque converter, or related components *could* contribute to stalling under deceleration. This is less likely, but possible.
* Vacuum leaks: As mentioned before, vacuum leaks can affect many engine systems, leading to stalling under various conditions.
Troubleshooting Steps:
1. Check the basics: Start with the easiest and cheapest checks: Inspect the fuel filter (replace if dirty), check the spark plugs and wires (replace if worn or damaged), and visually inspect the distributor cap and rotor (if applicable).
2. Listen for unusual noises: Listen carefully for any unusual noises coming from the engine, especially while slowing down.
3. Check engine codes: Use an OBD-II scanner to read any diagnostic trouble codes (DTCs) stored in the car's computer. These codes can pinpoint the problem area.
4. Professional Diagnosis: If you're not comfortable working on the car yourself, take it to a qualified mechanic for diagnosis and repair. They have the tools and expertise to accurately diagnose the problem.
Remember to be safe when working on your car. Disconnect the negative battery terminal before performing any work on the electrical system. If you're unsure about any repair, consult a professional mechanic.
