Hesitation, Sag, Stumble. Chevrolet Tracker

Hesitation, Sag, Stumble

Checks

Action

DEFINITION: The vehicle has a momentary lack of response when pushing down on the accelerator. The condition can occur at any vehicle speed. The condition is usually most severe when trying to make the vehicle move, as from a stop sign. The condition may cause the engine to stall if severe enough.

Preliminary Check

•	Refer to Powertrain On Board Diagnostic (OBD) System Check .

•	Refer to Symptoms .

Sensor Check

•	Check the performance of the MAF sensor. Refer to Diagnostic Aids in DTC P0101 Mass Air Flow (MAF) Sensor Performance .

•	Inspect the operation of the heated oxygen sensor (HO2S) 1. Refer to:

-	DTC P0131 HO2S Circuit Low Voltage Sensor 1

-	DTC P0132 HO2S Circuit High Voltage Sensor 1

-	DTC P0133 HO2S Slow Response Sensor 1

-	DTC P0134 HO2S Circuit Insufficient Activity Sensor 1

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Inspect for a shifted or fixed engine coolant temperature (ECT) sensor. Test the ECT sensor using the scan tool. Compare the engine coolant temperature with the ambient air temperature on a cold engine. If the engine coolant temperature is more than 5°C (9°F) more or less than the ambient air temperature, check for a high resistance in the coolant sensor circuit or the sensor itself. Refer to Temperature Versus Resistance .

Fuel System Checks

•	Check for a restricted fuel filter or incorrect fuel pressure. Refer to Fuel System Diagnosis .

•	Check the fuel injectors. Perform the Fuel Injector Coil Test Procedure and the Fuel Injector Balance Test Procedure. Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) and Fuel Injector Balance Test .

•	Check for water contamination of the fuel.

•	Check the TP sensor for binding or sticking. Voltage should increase at a steady rate as throttle moves toward Wide Open Throttle (WOT).

•	Check the MAP sensor for a quick response and accuracy.

•	Check the Evaporative Emission (EVAP) control system. Refer to Evaporative Emission Control System Diagnosis .

Ignition System Checks

•	Check for faulty spark plug wires at cylinders 1 and 3.

•	Check for cracked ignition coils boots at cylinders 2 and 4.

•	Check for fouled spark plugs.

Additional Checks

•	Check the Service Bulletins for any updates.

•	Check the generator output voltage.

•	Check the EGR valve operation. Refer to Exhaust Gas Recirculation (EGR) System Diagnosis

•	Check for any vacuum or air leaks after the MAF sensor.