Poor Fuel Economy

Check listed items as follows:

• Check oxygen sensor switching. See CHECKING OXYGEN SENSOR SWITCHING under ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING article.
• Check Powertrain Control Module (PCM) power and ground circuits. See POWERTRAIN CONTROL MODULE under COMPUTERIZED ENGINE CONTROLS in SYSTEM & COMPONENT TESTING article.
• Check engine vacuum. See CHECKING ENGINE VACUUM under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES article.
• Check fuel pressure. See FUEL PRESSURE TEST under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES article.
• Check engine coolant temperature sensor. See CHECKING ENGINE COOLANT TEMPERATURE SENSOR CALIBRATION under ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING article.
• Check throttle position sensor. See CHECKING THROTTLE POSITION SENSOR CALIBRATION under ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING article.
• On 2.5L and 4.0L, check minimum idle airflow. See CHECKING MINIMUM AIRFLOW (2.5L & 4.0L) under IDLE CONTROL SYSTEMS in SYSTEM & COMPONENT TESTING article.
• Check oxygen sensor switching. See CHECKING OXYGEN SENSOR SWITCHING under ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING article.
• Check heated oxygen sensor heater. See CHECKING OXYGEN SENSOR HEATER under ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING article.
• Check idle air control motor operation. See CHECKING IDLE AIR CONTROL MOTOR under IDLE CONTROL SYSTEMS in SYSTEM & COMPONENT TESTING article.
• Check engine mechanical systems. See CHECKING ENGINE MECHANICAL SYSTEMS under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES article.
• Check EVAP emission system. See FUEL EVAPORATIVE SYSTEM in SYSTEM & COMPONENT TESTING article.
• Check intake air temperature sensor. See CHECKING INTAKE AIR TEMPERATURE SENSOR under ENGINE SENSORS & SWITCHES in SYSTEM & COMPONENT TESTING article.