what to do if my Ford Mustang S550 (2015-2023) has a rough idle when cold

Solution

1. Preparation

• Ensure the vehicle is parked on a level surface and the engine is off.
• Gather necessary tools and parts.

2. Replace Spark Plugs

• Remove the engine cover, if applicable.
• Disconnect the ignition coils by unplugging the electrical connectors.
• Unscrew and remove the ignition coils using a socket set.
• Remove the old spark plugs using a spark plug socket and ratchet.
• Inspect the old spark plugs for any signs of wear or damage.
• Install new spark plugs, ensuring they are gapped to the manufacturer's specifications (typically 0.028-0.032 inches for Mustang).
• Reinstall the ignition coils and secure them with bolts.

3. Clean or Replace the IAC Valve

• Locate the IAC valve, typically found near the throttle body.
• Disconnect the electrical connector from the IAC valve.
• Remove the IAC valve using a socket set, being cautious not to damage the gasket.
• Clean the valve and its mounting surface with throttle body cleaner.
• If cleaning does not resolve the issue, replace the IAC valve with a new one.
• Reinstall the IAC valve and reconnect the electrical connector.

4. Inspect and Clean the MAF Sensor

• Locate the MAF sensor in the air intake duct.
• Disconnect the electrical connector.
• Remove the sensor from the duct using a screwdriver.
• Clean the sensor with MAF cleaner and a soft brush; do not touch the sensor element.
• Reinstall the MAF sensor and its connector.

5. Perform Fuel Pressure Test

• Locate the fuel pressure test port on the fuel rail.
• Connect the fuel pressure gauge to the test port.
• Turn the ignition to the 'On' position (do not start the engine) and check the pressure reading; it should be within the manufacturer's specified range (typically 40-60 psi).
• If the pressure is low, inspect the fuel pump and filter for issues.

Tools Required:

• OBD-II scanner
• Socket set
• Ratchet and extensions
• Spark plug socket
• Fuel pressure gauge
• Throttle body cleaner
• MAF cleaner
• Screwdrivers

Parts Required:

• Spark plugs
• Ignition coils (if damaged)
• Idle Air Control (IAC) valve (if necessary)
• Mass Air Flow (MAF) sensor cleaner

Estimated Repair Time: 2-4 hours

Safety Warnings:

• Disconnect the battery before working on electrical systems.
• Allow the engine to cool before servicing components.