Rough, Unstable, or Incorrect Idle and Stalling

WARNING: This page is about a different car, the 2004 Pontiac Grand Prix. However, it is still accessible from the selected car via links, so may be relevant.

Inspections	Action
DEFINITION: Engine runs unevenly at idle. If severe, the engine or vehicle may shake. Engine idle speed may vary in RPM. Either condition may be severe enough to stall the engine.
Preliminary Inspections	Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls . Search for bulletins. Inspect the powertrain control module (PCM) 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 restrictions. Refer to Air Cleaner Element Replacement . Replace as necessary.
Fuel System	Test the fuel injectors. Refer to Fuel Injector Balance Test with Special Tool , Fuel Injector Balance Test with Tech 2 , and Fuel Injector Coil Test . Inspect for incorrect fuel pressure. Refer to Fuel System Diagnosis . Inspect for a restricted fuel filter. Refer to Fuel System Diagnosis . Inspect for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) . Inspect that each fuel injector harness is connected to the correct injector/cylinder. Relocate fuel injector harnesses as necessary. Inspect for the following conditions that may cause the engine to run rich: NOTE: Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. Water intrusion in the HO2S connector Engine oil contaminated by fuel An EVAP canister purge condition Incorrect fuel pressure-Refer to Fuel System Diagnosis . Leaking fuel injectors-Refer to Fuel System Diagnosis . For proper operation of the manifold absolute pressure (MAP) sensor-Refer to Manifold Absolute Pressure (MAP) Sensor Diagnosis (With Supercharger) or Manifold Absolute Pressure (MAP) Sensor Diagnosis (Without Supercharger) . For proper operation of the mass air flow (MAF) sensor. Refer to Scan Tool Data Definitions and Scan Tool Data List . Blockage on the inlet screen of the MAF sensor Vacuum hoses that are split, kinked, or improperly connected An air intake duct that is collapsed or restricted An air filter that is dirty or restricted-Refer to Air Cleaner Element Replacement . Inspect for the following conditions that may cause the engine to run lean: NOTE: Refer to Heated Oxygen and Oxygen Sensor Notice in Cautions and Notices. Water intrusion in the HO2S connector An exhaust leak between the HO2S and the engine-Refer to Exhaust Leakage in Engine Exhaust. Vacuum leaks Incorrect fuel pressure-Refer to Fuel System Diagnosis . Restricted fuel injectors-Refer to Fuel Injector Balance Test with Special Tool and Fuel Injector Balance Test with Tech 2 . For proper operation of the manifold absolute pressure (MAP) sensor-Refer to Manifold Absolute Pressure (MAP) Sensor Diagnosis (With Supercharger) or Manifold Absolute Pressure (MAP) Sensor Diagnosis (Without Supercharger) . For proper operation of the mass air flow (MAF) sensor-Refer to Scan Tool Data Definitions and Scan Tool Data List . Fuel contamination-Refer to Alcohol/Contaminants-in-Fuel Diagnosis (With Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (Without Special Tool) . Vacuum hoses that are split, kinked, or improperly connected
Sensor/System	Inspect the air intake ducts for being collapsed, damaged areas, looseness, improper installation, or leaking especially between the MAF sensor and the throttle body. Inspect the exhaust gas recirculation (EGR) system for proper operation. Refer to Exhaust Gas Recirculation (EGR) System Description . Inspect the Transaxle Range Switch input with the vehicle in drive and the gear selector in drive or overdrive. Inspect the crankcase ventilation valve for proper operation. Use a scan tool in order to monitor the knock sensor (KS) system for excessive spark retard activity.
Ignition System	Inspect for proper ignition voltage output with the J 26792 Spark Tester. Refer to Electronic Ignition (EI) System Diagnosis . Remove spark plugs and inspect for the following conditions: Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits In order to properly inspect the spark plugs or to correct a condition, refer to the following procedures: Ignition System Specifications Spark Plug Inspection Spark Plug Replacement An improper spark plug gap will cause a driveability problem. Gap the spark plugs using a wire gauge gap tool. Determine the cause of the fouling before replacing the spark plugs. Inspect the spark plug wires for signs of arcing/cross firing, cracks, carbon tracking, plug boot damage, pinched, improper routing, or a resistance value outside the specified range. Refer to Ignition System Specifications . Soak the secondary ignition system with water from a spray bottle. Soaking the secondary ignition system may help locate damaged or deteriorated components. Look and listen for arcing or misfiring as you apply water. Monitor the Misfire Current Counters while driving the vehicle in the conditions that the misfire occurred. If a misfiring cylinder can be located, use the DTC P0300 table for diagnosis. Refer to DTC P0300 . Inspect for loose ignition coil grounds.
Engine Mechanical	Inspect engine mechanical for the following conditions: Compression Sticking or leaking valves Worn camshaft lobes Valve timing Bent push rods Worn rocker arms Broken valve springs Excessive oil in combustion chamber or leaking valve seals For more information, refer to one or more of the following procedures in Engine Mechanical Engine Compression Test Symptoms - Engine Mechanical Oil Consumption Diagnosis For incorrect basic engine parts. Inspect the following components: The camshaft-Refer to Camshaft and Bearings Cleaning and Inspection in Engine Mechanical. The cylinder heads-Refer to Cylinder Head Cleaning and Inspection in Engine Mechanical. The pistons, etc.-Refer to Piston, Connecting Rod, and Bearings Cleaning and Inspection in Engine Mechanical.
Additional Inspections	Inspect the exhaust system for possible restrictions. Inspect for the following conditions: The exhaust system for damaged or collapsed pipes The mufflers for heat distress or possible internal failure For possible plugged catalytic converters-Refer to Restricted Exhaust in Engine Exhaust. Electromagnetic interference (EMI) on the 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 change indicates that EMI is present. If a problem exists, inspect routing of secondary ignition wires or high voltage components near the ignition control circuits. Inspect for faulty motor mounts. Refer to Engine Mount Inspection in Engine Mechanical. Inspect the intake manifold and the exhaust manifold passages for casting flash. Inspect for an exhaust gas recirculation (EGR) valve stuck open or EGR pintle not seating properly. Inspect EGR valve gasket for leaks.