Additional Symptoms Tests

Detonation/Spark Knock Test the engine for an overheating condition. Refer to ENGINE OVERHEATING .

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 INSPECTION .

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. Refer to TEMPERATURE VERSUS RESISTANCE - ENGINE COOLANT TEMPERATURE SENSOR for resistance specifications. 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 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 fuel pressure. Refer to FUEL SYSTEM DIAGNOSIS .
Test the generator. Refer to SYMPTOMS - ENGINE ELECTRICAL . Repair the charging system if the generator output voltage is less than 9 volts or more 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.