Rough, Unstable, or Incorrect Idle and Stalling

WARNING: This page is about a different variant/trim than selected.

Inspections	Action
DEFINITION: The engine runs unevenly at idle. If severe, the engine or the vehicle may shake. Engine idle speed may vary in RPM. Either condition may be severe enough to stall the engine.
Preliminary	Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls . Search for bulletins. Inspect the engine control module (ECM) grounds for being clean, tight, and in the proper locations. Refer to Power and Grounding Component Views in Wiring Systems and Engine Controls Schematics . Remove and inspect the air filter element for dirt or for being restricted. Refer to Air Cleaner Element Replacement .
Fuel System	Test the fuel injectors. Refer to Fuel Injector Coil Test . Inspect the fuel system. Refer to Fuel System Diagnosis . Test for incorrect fuel pressure. Test for a restricted fuel filter. Test for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (w/o Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (w/ Special Tool) . Confirm that each injector harness is connected to the correct injector/cylinder. Relocate the injector harnesses as necessary. Inspect for items which can cause an engine to run rich, long term fuel trim near -13 percent. For a rich condition, refer to DTC P0172 or P0175 . Inspect for items that can cause an engine to run lean, long term fuel trim near 23 percent. For a lean condition, refer to DTC P0171 or P0174 .
Sensor/System	Test the crankcase ventilation system. Refer to Crankcase Ventilation System Inspection/Diagnosis in Engine Mechanical. Test the crankcase ventilation valve for proper operation. Place a finger over the inlet hole of the valve end several times. The valve should snap back. If not, replace the valve. Refer to Crankcase Vent Housing Replacement in Engine Mechanical. Monitor the knock sensor (KS) system for excessive spark retard activity with a scan tool. Refer to Scan Tool Data List .
Ignition System	Test for proper ignition system operation. Refer to Electronic Ignition (EI) System Diagnosis . Remove the spark plugs and inspect for the following conditions: Correct heat range Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Determine the cause of the fouling before replacing the spark plugs if the spark plugs are gas, coolant or oil fouled. Refer to Spark Plug Inspection . Once you determine the cause of the fouling, refer to one of the following procedures: For diagnosis of a rich condition, refer to DTC P0172 or P0175 . For diagnosis of coolant contaminated spark plugs, refer to Loss of Coolant (M 35) or Loss of Coolant (M 82) in Engine Cooling. For diagnosis of oil fouled spark plugs, refer to Oil Consumption Diagnosis in Engine Mechanical.
Engine Mechanical	Inspect engine mechanical for the following conditions: Low compression-Refer to Engine Compression Test in Engine Mechanical. Sticking or leaking valves Worn camshaft lobes-Refer to Camshaft and Bearings Cleaning and Inspection in Engine Mechanical. Camshaft timing-Refer to Timing Belt Timing Procedure in Engine Mechanical. Broken valve springs Excessive oil in combustion chamber-Leaking valve seals-Refer to Oil Consumption Diagnosis in Engine Mechanical. Inspect the following components for incorrect basic engine parts: Camshaft-Refer to Camshaft and Bearings Cleaning and Inspection in Engine Mechanical. Cylinder heads-Refer to Cylinder Head Cleaning and Inspection in Engine Mechanical. Pistons, connecting rods, or bearings-Refer to Piston, Connecting Rod, and Bearings Cleaning and Inspection in Engine Mechanical.
Additional	Inspect the exhaust system for the following possible restrictions: The exhaust system components for physical damage The catalytic converters for possible plugged pipes by comparing the exhaust system back pressure on each side of engine-Refer to Restricted Exhaust in Engine Exhaust. Electromagnetic interference (EMI) on the CKP reference circuit can cause an engine miss condition. A scan tool can usually detect EMI by monitoring the engine RPM. A sudden increase in RPM with little change in actual engine RPM indicates that EMI is present. If a condition exists, inspect for high voltage components near ignition control circuits. Inspect for faulty engine mounts. Refer to Engine Mount Replacement - Left or Engine Mount Replacement - Right in Engine Mechanical. Inspect the intake manifold and the exhaust manifold passages for casting flash. Refer to: Intake Manifold Replacement in Engine Mechanical Exhaust Manifold Replacement - Left (LY7) , Exhaust Manifold Replacement - Left (LA3, LY9) or Exhaust Manifold Replacement - Left (LS6) in Engine Exhaust Exhaust Manifold Replacement - Right (LA3, LY9) , Exhaust Manifold Replacement - Right (LY7) or Exhaust Manifold Replacement - Right (LS6) in Engine Exhaust