Hesitation, Sag, Stumble

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

Inspections	Action
DEFINITION: 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.
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 .
Sensor/System	Test the heated oxygen sensors (HO2S). The HO2S should respond quickly to the different throttle positions. If they do not, inspect the HO2S for silicon or other contaminates from fuel or the use of improper RTV sealant. The sensors may have a white powdery coating. This type of contamination may result in a rich exhaust indication. The ECM will then reduce the amount of fuel delivered to the engine, causing a severe driveability condition. Inspect the mass air flow (MAF) sensor connections. Repair or replace the terminals as necessary. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Inspect the CMP sensor for proper operation or intermittent conditions. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Inspect the CKP sensor for proper operation or intermittent conditions. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Verify the proper operation of the TAC system by performing the following procedure: Observe the TP sensor angle with a scan tool. Slowly depress the accelerator pedal to wide open throttle (WOT) with the key ON and the engine OFF, then slowly return the pedal to the rest position. The TP sensor angle should increase to near 100 percent as the pedal is depressed and decrease as the pedal is released. A verification of the entire TAC system is being performed by performing this test.
Fuel System	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) . Test the fuel injectors. Refer to Fuel Injector Coil Test . Inspect the 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 the 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 .
Ignition System	Test for proper ignition system operation. Refer to Electronic Ignition (EI) System Diagnosis . Test for secondary ignition system leakage. 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 Cooling System	Test the engine thermostat for proper operation and correct heat range. Refer to Thermostat Diagnosis (LA3, LY9) , Thermostat Diagnosis (LY7) or Thermostat Diagnosis (LS6) in Engine Cooling.
Additional	Test the generator output voltage. Refer to Diagnostic System Check - Engine Electrical in Engine Electrical. Repair the charging system if the generator output voltage is less than 9 volts or more than 16 volts.