Hesitation, Sag, Stumble. Chevrolet Tracker

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 2004 🢒 Tracker - 4WD 🢒 Engine 🢒 Engine Controls - 2.5L (LE8) 🢒 Hesitation, Sag, Stumble

Checks

Action

DEFINITION: The vehicle has a momentary lack of response when accelerating. The condition can occur at any vehicle speed. The condition is usually most noticeable when accelerating from a stop. The condition may cause the engine to stall in severe cases.

Preliminary Check

•	Refer to Diagnostic System Check - Engine Controls .

•	Refer to Symptoms - Engine Controls .

Sensor Check

•	Check the performance of the mass air flow (MAF) sensor. Refer to DTC P0101 .

•	Inspect the performance of the heated oxygen sensors (HO2S) 1. Refer to:

-	DTC P0131 or P0151

-	DTC P0132 or P0152

-	DTC P0133 or P0153

-	DTC P0134 or P0154

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Check the throttle position (TP) sensor. A sticking throttle shaft or a binding throttle linkage will cause a high TP sensor voltage or an open throttle indication. Under these conditions the powertrain control module (PCM) may not control the idle. Monitor the TP sensor voltage with the scan tool or a DMM. The indicated voltage should be less than 1.0 volts with the throttle closed.

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Inspect for a shifted or fixed engine coolant temperature (ECT) sensor. With a scan tool, compare the engine coolant temperature of a cold engine with the ambient air temperature. A difference of more than 5°C (9°F) may indicate high resistance in the coolant sensor circuit or the sensor. 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 .

•	Inspect the fuel injectors for correct operation and performance. Refer to Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F) and Fuel Injector Balance Test with Special Tool .

•	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. Refer to Electronic Ignition (EI) System Diagnosis .

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

•	Check for damaged or worn spark plugs. Refer to Spark Plug Inspection .

•	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 .

•	Check the Service Bulletins for any updates.