how to fix rough idle at stop lights in GMC Sierra T1XX (2019-Present)?

Learn how to fix rough idle at stop lights in GMC Sierra T1XX (2019-Present). Step-by-step guide with diagnostic procedures and repair instructions.

Solution

1. Preparation

• Gather all tools and parts required for the repair.
• Ensure the vehicle is parked on a flat surface and the engine is cooled down.
• Disconnect the negative battery terminal to prevent electrical shorts.

2. Inspect and Replace Spark Plugs

1. Remove Engine Cover: If applicable, remove the engine cover by unscrewing any retaining bolts.
2. Access Spark Plugs: Use a socket set to remove the ignition coils by unscrewing the bolts and gently pulling them out of the spark plug wells.
3. Remove Spark Plugs: Using a spark plug socket, carefully unscrew the old spark plugs.
4. Install New Spark Plugs: Apply anti-seize lubricant to the threads of new spark plugs, then install them by hand to avoid cross-threading before tightening to the manufacturer's specified torque (typically around 12-15 ft-lbs).
5. Reinstall Ignition Coils: Reinsert the ignition coils and secure them with their bolts. Reconnect the electrical connectors.

3. Clean Throttle Body

1. Remove Air Intake Hose: Loosen the clamps and disconnect the air intake hose from the throttle body.
2. Access Throttle Body: If needed, remove additional components to gain access to the throttle body.
3. Clean Throttle Body: Using throttle body cleaner and a clean rag, clean the throttle plate and the surrounding area. Ensure no cleaner residue enters the intake manifold.
4. Reassemble Components: Reconnect the air intake hose and ensure all clamps are secured.

4. Check and Repair Vacuum Leaks

1. Inspect Vacuum Hoses: Visually check all vacuum hoses for cracks, wear, or disconnections.
2. Replace Damaged Hoses: If any hoses are damaged, replace them with new ones.
3. Test for Leaks: If necessary, use a smoke machine or propane torch (with no flame) around hoses to detect leaks.

5. Reset the Engine Control Module (ECM)

1. Reconnect Battery: Reattach the negative battery terminal.
2. Clear Codes: Use the OBD-II scanner to clear any fault codes from the ECM.
3. Test Drive: Take the vehicle for a test drive to allow the ECM to relearn idle parameters.