Hesitation, Sag, Stumble. Chevrolet Tracker

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 2000 🢒 Tracker - 4WD 🢒 Engine 🢒 Engine Controls - 2.0L 🢒 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 mass air flow (MAF) sensor. Refer to DTC P0101 Mass Air Flow (MAF) Sensor Performance .

•	Inspect the performance of the heated oxygen sensors (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 restriction in the fuel supply system. Check for the correct fuel pressure. Refer to Fuel System Diagnosis .

•	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.

Ignition System Checks

•	Check for adequate secondary ignition voltage with a J 26792 spark tester or an equivalent.

•	Check for the correct ignition timing. Refer to Ignition Timing Adjustment .

•	Check the spark plugs for any of the following conditions:

-	Any wet plugs

-	A terminal screw that is bent or loose

-	A ceramic insulator that has cracks, carbon tracking or deposits

-	A tip insulator that has cracks, carbon tracking, deposits, or is loose

-	A center electrode that is loose

-	An incorrect spark plug gap that is too large or too small

•	Check the ignition coil spark plug boots for cracks, carbon tracking, and moisture.

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Check the engine reference signal of the camshaft position (CMP) sensor with a scan tool. Observe the Engine Speed parameter while operating the engine at the speed of the concern. The scan tool should indicate steady and linear RPM readings while running. If the erratic values, such as sudden spikes or drops in engine speed are displayed, the engine reference signal is not stable enough for the engine to run properly. Inspect the CMP sensor signal rotor and housing for worn bushings or drive coupling. Inspect for electromagnetic interference (EMI) of the reference signal.

Additional Checks

•	Check the throttle position (TP) sensor for binding or sticking. The voltage should increase at a steady rate as the throttle moves toward wide open throttle (WOT).

•	Check the manifold air pressure (MAP) sensor for a quick and accurate response to changes in the intake manifold pressure.

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

•	Check the generator output voltage.

•	Check for excessive exhaust system backpressure. Refer to Restricted Exhaust System Check .

•	Check the Service Bulletins for any updates.