Symptoms - Engine Controls: Symptoms

WARNING: This page is about a different car, the 2006 Pontiac Montana SV6, 2006 Chevrolet Uplander, and 2006 Buick Terraza. However, it is still accessible from the selected car via links, so may be relevant.

Hard Start: Engine cranks OK, but does not start for a long time. Does eventually run or may start but immediately stalls.
Surges/Chuggles: Engine power variation under steady throttle or cruise. Feels like the vehicle speeds up and slows down without a change in the accelerator pedal position.
Lack of Power, Sluggishness or Sponginess: The engine delivers less than expected power. Little increase in speed or a total lack of acceleration when the accelerator pedal is pushed down part way.
Detonation/Spark Knock: A mild to severe ping which usually occurs worse while under acceleration. The engine makes sharp metallic knocks that change with throttle opening.
Hesitation, Sag, Stumble: Momentary lack of response as the accelerator is pushed down. This condition can occur at any vehicle speed. This condition is usually more pronounced when first trying to make the vehicle move, as from a stop sign. This condition may cause the engine to stall if severe enough.
Cuts Out, Misses: A steady pulsation or jerking that follows engine speed, which is usually more pronounced as the engine load increases. This condition is not normally felt above 1,500 RPM or 48 km/h (30 mph). The exhaust has a steady spitting sound at idle or at low speed.
Poor Fuel Economy: Fuel economy, as measured by an actual road test, is noticeably lower than expected. Also, the fuel economy is noticeably lower than it was on this vehicle at one time, as previously shown by an actual road test.
Rough, Unstable or Incorrect Idle and Stalling: The engine runs unevenly at idle. If severe, the engine or the vehicle may shake. Engine idle may vary in speed. Either condition may be severe enough to stall the engine.
Dieseling, Run-On: The engine continues to run after the key is turned OFF, but runs very rough. If the engine runs smooth, inspect the ignition switch and the ignition switch adjustment.
Backfire: Fuel ignites in the intake manifold or in the exhaust system, making a loud popping noise.

Use the following symptoms in order to isolate possible systems that are associated with the condition:

Symptoms

Symptoms	Action/System
Find the symptom in the left column and perform the test/inspection procedure in the right column
Hard Start Backfire	Tip: A vehicle with a camshaft actuator stuck in an un-parked position may experience a hard start. Start and run the engine until fully warm. Observe the camshaft position (CMP) variation parameter while accelerating up to 1,500 RPM and back to idle several times. The CMP variation should indicate a value for 1-2 seconds and then return to 0 degree. If the camshaft actuator does not respond, refer to Camshaft Position Actuator Cleaning and Inspection and Camshaft Position Actuator Magnet Cleaning and Inspection . Symptoms - Fuel System Symptoms - Ignition System Symptoms - Sensors/Systems Engine exhaust-Refer to Symptoms - Engine Exhaust . Inspect the engine mechanical for oil consumption, correct engine compression and correct base engine timing-Refer to Symptoms - Engine Mechanical . Backfire-Inspect the intake and exhaust system and associated passages for casting flash. Inspect the engine cooling system for correct level and operation-Refer to Symptoms - Engine Cooling . Inspect the engine electrical system for correct operation-Refer to Charging System Test .
Surges/Chuggles	Tip: A vehicle with a camshaft actuator uncontrolled and wandering may experience an engine surge. Start and run the engine until fully warm. Observe the CMP variation parameter while accelerating up to 1,500 RPM and back to idle several times. The CMP variation should indicate a value for 1-2 seconds and then return to 0 degree. If the camshaft actuator does not respond, refer to Camshaft Position Actuator Cleaning and Inspection and Camshaft Position Actuator Magnet Cleaning and Inspection . Symptoms - Fuel System Symptoms - Ignition System Symptoms - Sensors/Systems Inspect the engine mechanical for oil consumption, correct engine compression and correct base engine timing-Refer to Symptoms - Engine Mechanical . Inspect the engine mechanical for correct engine oil pressure. Incorrect oil pressure may cause the camshaft actuator to vary beyond the device control when operated. Refer to Oil Pressure Diagnosis and Testing . Inspect the engine electrical system for correct operation-Refer to Charging System Test . Engine exhaust-Refer to Restricted Exhaust . Ensure the customer understands the operation of the Automatic Transmission including the Tap shift option if applicable. Inspect the automatic transmission for proper shifting and torque converter clutch (TCC) engagement-Refer to Symptoms - Automatic Transmission . HVAC System operation- Ensure the customer understands the operation of the HVAC system. Refer to the following: Air Conditioning (A/C) System Performance Test Symptoms - HVAC Systems - Manual Symptoms - HVAC Systems - Automatic
Lack of Power, Sluggishness or Sponginess	Tip: A vehicle with a camshaft actuator stuck in the park position may experience a lack of power during take off. Start and run the engine until fully warm. Observe the CMP variation parameter while accelerating up to 1,500 RPM and back to idle several times. The CMP variation should indicate a value for 1-2 seconds and then return to 0 degree. If the camshaft actuator does not respond, refer to Camshaft Position Actuator Cleaning and Inspection and Camshaft Position Actuator Magnet Cleaning and Inspection . Symptoms - Fuel System Symptoms - Ignition System Symptoms - Sensors/Systems Inspect for a restricted air intake system. Inspect for a dirty or restricted air filter. Inspect the engine mechanical for oil consumption, correct engine compression and correct base engine timing-Refer to Symptoms - Engine Mechanical . Inspect the engine mechanical for correct engine oil pressure. Incorrect oil pressure may cause the camshaft actuator to vary beyond the device control when operated. Refer to Oil Pressure Diagnosis and Testing . Inspect the engine electrical system for correct operation-Refer to Charging System Test . Engine Exhaust-Refer to Restricted Exhaust . Ensure the customer understands the operation of the Automatic Transmission including the Tap shift option if applicable. Inspect the automatic transmission for proper shifting and TCC engagement-Refer to Symptoms - Automatic Transmission . Torque Management System, if applicable-Refer to CELL LINK ABS Description and Operation and Symptoms - Antilock Brake System . HVAC System operation-Refer to the following: Air Conditioning (A/C) System Performance Test Symptoms - HVAC Systems - Manual Symptoms - HVAC Systems - Automatic .
Hesitation, Sag, Stumble Cuts Out, Misses Rough, Unstable or Incorrect Idle and Stalling	IMPORTANT: A rough idle may be considered a normal condition at start-up if the engine oil temperature is below -7°C (+19.4°F). This condition may last up to 200 seconds until the oil temperature warms enough to allow stable operation of the camshaft actuator. Tip: A vehicle with a camshaft actuator stuck at full camshaft retard may experience a rough idle.Start and run the engine until fully warm. Observe the CMP variation parameter while accelerating up to 1,500 RPM and back to idle several times. The CMP variation should indicate a value for 1-2 seconds and then return to 0 degree. If the camshaft actuator does not respond, refer to Camshaft Position Actuator Cleaning and Inspection and Camshaft Position Actuator Magnet Cleaning and Inspection . Symptoms - Fuel System Symptoms - Ignition System Symptoms - Sensors/Systems Inspect for a restricted air intake system. Inspect for a dirty or restricted air filter. Ensure correct engine oil is used. Incorrect oil for the temperature may cause variations with camshaft actuator operation. Inspect the intake manifold tuning valve for leaks at the seal and for proper operation. An uncontrolled tuning valve may cause isolations in the air flow-refer to intake manifold tuning valve inspection in the Intake Manifold Replacement - Upper . Inspect the engine mechanical for oil consumption, correct engine compression and correct base engine timing-Refer to Symptoms - Engine Mechanical . Inspect the engine mechanical for correct engine oil pressure. Incorrect oil pressure may cause the camshaft actuator to vary beyond the device control when operated. Refer to Oil Pressure Diagnosis and Testing . Inspect the engine electrical system for correct operation-Refer to Charging System Test . Engine Cooling System-Refer to Symptoms - Engine Cooling . Engine Exhaust-Refer to Restricted Exhaust . Inspect the engine mounts. Refer to Engine Mount Inspection . Inspect the crankcase ventilation system-Refer to Positive Crankcase Ventilation (PCV) Valve Cleaning and Inspection . Inspect the air intake system for leaks and unmetered air HVAC System operation-Refer to the following: Air Conditioning (A/C) System Performance Test Symptoms - HVAC Systems - Manual Symptoms - HVAC Systems - Automatic Inspect the automatic transmission for proper shifting and TCC engagement-Refer to Symptoms - Automatic Transmission . Inspect the transmission range switch for proper operation. Refer to Range Selector Displays Incorrect Range (3.5L) or Range Selector Displays Incorrect Range (3.9L) . Inspect the transmission mounts. Refer to CELL LINK 142106 for the F40 transmission or Transmission Mount Inspection for the 4T65E transmission.
Detonation/Spark Knock	Excessive heavy loads or review owner's driving habits-Consult the Vehicle Owner's Manual. Ensure quality fuel is used-Consult the Vehicle Owner's Manual Symptoms - Fuel System Symptoms - Ignition System Inspect the engine mechanical for the following: Oil consumption Carbon build up or other hot point within the combustion chamber Correct engine compression Correct base engine timing Refer to Symptoms - Engine Mechanical . Engine Cooling System-Refer to Engine Overheating . Inspect the automatic transmission for proper shifting and TCC engagement-Refer to Symptoms - Automatic Transmission .
Poor Fuel Economy	Proper tire inflation-Refer to Tires in Service and Appearance Care in the vehicle Owner's Manual. Inspect for a dirty or restricted air filter. Fuel Quality-Refer to the following: Alcohol/Contaminants-in-Fuel Diagnosis Fuel Service and Appearance Care in the vehicle Owner's Manual Symptoms - Fuel System Symptoms - Ignition System Symptoms - Sensors/Systems Inspect the engine mechanical for oil consumption, correct engine compression and correct base engine timing-Refer to Symptoms - Engine Mechanical . Inspect the crankcase ventilation system-Refer to Positive Crankcase Ventilation (PCV) Valve Cleaning and Inspection . Tip: A vehicle with a camshaft actuator either stuck at full camshaft retard, in the park position or uncontrolled and wandering may experience poor fuel economy. Start and run the engine until fully warm. Observe the CMP variation parameter while accelerating up to 1,500 RPM and back to idle several times. The CMP variation should indicate a value for 1-2 seconds and then return to 0 degree. If the camshaft actuator responds erratic or inconsistent or not at all, refer to Camshaft Position Actuator Cleaning and Inspection and Camshaft Position Actuator Magnet Cleaning and Inspection . Inspect the engine cooling system for correct level and operation-Refer to Symptoms - Engine Cooling . Engine Electrical System operation-Refer to Charging System Test . Engine Exhaust-Refer to Symptoms - Engine Exhaust . HVAC System operation. Ensure the customer understands the operation of the HVAC system-Refer to the following: Air Conditioning (A/C) System Performance Test Symptoms - HVAC Systems - Manual Symptoms - HVAC Systems - Automatic . Ensure the customer understands the operation of the Automatic Transmission including the Tap shift option if applicable. Inspect the automatic transmission for proper shifting and TCC engagement-Refer to Symptoms - Automatic Transmission . Inspect the Braking System-Refer to BRAKES DRAG .
Dieseling/Run-On	Symptoms - Fuel System Symptoms - Ignition System Inspect the engine mechanical for the following: Carbon build up or other hot point within the combustion chamber Correct engine compression Correct base engine timing Refer to Symptoms - Engine Mechanical . Inspect the intake and exhaust system and associated passages for casting flash.