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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2000 🢒 Alero Export 🢒 Engine 🢒 Engine Controls - 2.4L 🢒 Hesitation, Sag, Stumble

Hesitation, Sag, Stumble

Tests/inspections

Action

DEFINITION: Momentary lack of response as the accelerator is pushed down. Can occur at any vehicle speed. Usually more pronounced when first trying to make the vehicle move, as from a stop sign. May cause the engine to stall if severe enough.

Preliminary
    • Refer to Symptoms .
    • Search for service bulletins.

Sensor/System
    • Test for correct operation of the manifold absolute pressure (MAP) sensor. Refer to Manifold Absolute Pressure Sensor Output Diagnosis .
    • Test for correct operation of the throttle position (TP) sensor.
    • Test for correct operation of the engine coolant temperature (ECT) sensor.
    • Test the oxygen sensor (O2S 1). The O2S 1 should respond quickly to different throttle positions. If not, inspect the O2S 1 for silicon or other contaminants from fuel or the use of improper RTV sealant. The sensor may have a white powdery coating. Silicon contamination causes a high but false O2S 1 signal voltage (rich exhaust indication). The PCM will reduce the amount of fuel delivered to the engine, causing a severe driveability problem. Refer to Information Sensors/Switches Description .

Fuel System
    • Test the fuel pressure. Refer to Fuel System Diagnosis .
    • Test for a contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Test the fuel injectors. Refer to Fuel Injector Balance Test .
    • Inspect the items which can cause an engine to run rich (long term fuel trim is significantly in the negative range). Refer to Diagnostic Aids for DTC P0172 Fuel Trim System Rich .
    • Inspect the items that can cause an engine to run lean (long term fuel trim is significantly in the positive range). Refer to Diagnostic Aids for DTC P0171 Fuel Trim System Lean .
    • Test for the correct operation of the evaporative emission (EVAP) control system. Refer to Evaporative Emission Control System Diagnosis .

Ignition System
    • Test for the correct ignition voltage output.
    • Inspect the spark plugs for the following conditions:
       - Any wet or fuel fouled plugs
       - Any cracks
       - An incorrect gap
       - Any burnt electrodes or heavy deposits
    • If the spark plugs are fuel or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.
    • Inspect the ignition control module (ICM) for the correct ground connection.
    • Inspect the ignition coils for cracks or carbon tracking.

Additional
    • Test for the correct operation of the automatic transaxle. Refer to Road Test in Automatic Transaxle.
    • Test the generator output voltage. Refer to Diagnostic System Check - Engine Electrical in Engine Electrical.

If all procedures have been completed and no malfunctions have not been found, test and inspect all of the connections within the suspected circuit and systems.

Observe all scan tool data for the suspected circuit and systems.