Additional Symptoms Tests

Detonation/Spark Knock: Test the engine for an overheating condition. Refer to Symptoms - Engine Cooling .
Lack of Power, Hesitation, or Cut Out: Test for the correct operation of the intake manifold tuning (IMT) valve system. Refer to Intake Manifold Tuning Valve Diagnosis .
Poor Fuel Economy: Inspect for foreign material accumulation in the throttle bore, and for carbon deposits on the throttle plate and shaft. Also inspect for throttle body tampering.
Rough, Unstable, or Incorrect Idle and Stalling: Inspect the engine mounts. Refer to Engine Mount Replacement .
Surges/Chuggles: Test the heated oxygen sensors (HO2S). The HO2S should respond quickly to a change in throttle position. If the HO2S do not respond to different throttle positions, inspect for contamination from fuel, silicon, or the incorrect use of RTV sealant. The sensors may have a white powdery coating and result in a high, but false, signal voltage, which gives a rich exhaust indication. The ECM reduces the amount of fuel delivered to the engine, causing a driveability condition.

Hard Start

Test the engine coolant temperature (ECT) sensor. Compare the ECT sensor value to the intake air temperature (IAT) sensor value on a cold engine. The ECT and IAT sensor values should be within ± 3°C (5°F). If the ECT sensor is out of range with the IAT sensor, test the resistance of the ECT sensor. Replace the ECT sensor if the resistance is not within specification. Refer to Engine Coolant Temperature Sensor Replacement . If the sensor is within the specification, test the ECT circuits for a high resistance.
Test the idle air control (IAC) system. Refer to DTC P0506 or P0507 .
Test the fuel pump relay operation. The fuel pump should turn ON for 2 seconds when the ignition is turned ON. Refer to Fuel Pump Electrical Circuit Diagnosis .

Hesitation, Sag, Stumble

Test the manifold absolute pressure (MAP) sensor. Refer to DTC P0107 or P0108 .
Test the generator. Refer to Symptoms - Engine Electrical . Repair the charging system if the generator output voltage is less than 9 volts or greater than 16 volts.

Poor Fuel Economy

Heavy loads being carried or towed.
Acceleration rate too much or too often.
Inspect for foreign material accumulation in the throttle bore, and for carbon deposits on the throttle plate and shaft. Also inspect for throttle body tampering.