Rough, Unstable, or Incorrect Idle and Stalling

WARNING: This page is about a different car, the 2007 Isuzu i-370, 2007 GMC Canyon, and 2007 Chevrolet Colorado. 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 Beginning . 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 . Remove and inspect the air filter element for dirt or for restrictions. Refer to Air Cleaner Element Replacement . Replace as necessary.
Fuel System	Inspect the fuel injectors. Refer to Fuel System Diagnosis . 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 (w/Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (w/o 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 that may cause the engine to run rich: NOTE: Refer to Heated Oxygen and Oxygen Sensor Notice . Water intrusion in the heated oxygen sensor (HO2S) connector Purging of a saturated evaporative emission (EVAP) canister Incorrect fuel pressure-Refer to Fuel System Diagnosis . A leaking fuel pressure regulator-Refer to Fuel System Diagnosis . Leaking fuel injectors-Refer to Fuel System Diagnosis . 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 . Water intrusion in the HO2S connector An exhaust leak between the HO2S and the engine-Refer to Exhaust Leakage . Vacuum leaks Incorrect fuel pressure-Refer to Fuel System Diagnosis . Restricted fuel injectors-Refer to Fuel Injector Diagnosis (w/CH47976) or Fuel Injector Diagnosis (w/J39021 or w/Tech 2) . Fuel contamination-Refer to Alcohol/Contaminants-in-Fuel Diagnosis (w/Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (w/o Special Tool) . Vacuum hoses that are split, kinked, or improperly connected
Sensor/System	Test for conditions which cause an incorrect idle speed. Throttle body tampering, excessive deposits, or damage Restricted air intake system Large vacuum leak Inspect the crankcase ventilation system for proper operation. Monitor the knock sensor (KS) system for excessive spark retard activity with a scan tool.
Ignition System	In order to properly inspect the spark plugs or to correct a condition, refer to the following procedures: Ignition System Specifications Spark Plug Replacement Spark Plug Inspection Inspect for proper secondary ignition voltage output with the J 26792 HEI Spark Tester. An improper spark plug gap will cause a driveability condition. Gap the spark plugs using a wire gage gap tool. If the spark plugs are found to be fouled, determine the cause before replacing the spark plugs. Inspect for damaged or misaligned spark plug boots. Monitor the Misfire Current Counters while driving the vehicle in the conditions that the symptom occurred. If a misfiring cylinder can be located, use the DTC P0300 table for diagnosis. Refer to DTC P0300 .
Engine Mechanical	Inspect engine mechanical for the following: Compression Sticking or leaking valves Worn camshaft lobes Valve timing 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: Engine Compression Test Engine Compression Test Oil Consumption Diagnosis For incorrect, worn, or damaged basic engine parts, inspect the following: The camshaft-Refer to Camshafts Cleaning and Inspection . The cylinder heads-Refer to Cylinder Head Cleaning and Inspection . The pistons, etc.-Refer to Piston, Connecting Rod, and Bearings Cleaning and Inspection .
Additional Inspections	Inspect the exhaust system for possible restrictions. Inspect for the following: The exhaust system for damaged or collapsed pipes The mufflers for heat distress or possible internal failure Possible plugged catalytic converters-Refer to Restricted Exhaust . Electromagnetic interference (EMI) on the reference circuit can cause an engine misfire condition. A scan tool can usually detect EMI by monitoring the engine RPM. A sudden increase in RPM parameter with little change in actual engine RPM change indicates that EMI is present. If a condition 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 . Inspect the intake manifold and the exhaust manifold passages for casting flash.