Symptom Procedure Definition

The following are steps to be taken to help determine and rectify the cause of specific symptoms.

Ensure fuel pressure is within specification. See BASIC TESTING article.
Test fuel injectors. See SYSTEM/COMP TESTS article.
Inspect throttle body ports and valves for deposits, wear or plugging. Clean or replace as necessary.
Check for spark using spark tester. See BASIC TESTING article.
Check idle speed components. Refer to IDLE SPEED SYSTEM in I - SYSTEM/COMP TEST article.
Ensure that battery is fully charged and maintains at least 9.6 volts while cranking.
Check spark plug for improper gap or fouling.
Ensure there are no vacuum leaks into intake system.
Check fast idle system components. See IDLE SPEED SYSTEM in I - SYSTEM/COMP TEST article. On Q45, ensure fast idle cam keeps cam follower is fully released. If not check adjustment. See ADJUSTMENTS article.
Check EGR valve operation. See I - SYSTEM/COMP TEST article.
Check EGR solenoid valve operation. See I - SYSTEM/COMP TEST article.
Ensure engine has adequate compression. See BASIC TESTING article.
Disconnect exhaust gas sensor and monitor change in driveability. If it improves, replace sensor. If not, go to 16.
Remove canister purge line from intake and test drive vehicle.
Remove vacuum hose from fuel pressure regulator and monitor for symptom change.
Enter self-diagnostic Mode II and monitor exhaust gas sensoroperation. See FEEDBACK SYSTEM in I - SYSTEM/COMP TEST article.
Check ECU harness connector.
Substitute a known good ECU.
Check ECU power supply and ground circuit. See POWER CIRCUITS and GROUND CIRCUITS in I - SYSTEM/COMP TEST article.
Check timing belt for proper installation.
Check throttle linkage operation.
Substitute a known good airflow meter.
Check for intake valve deposits.
Check coolant (engine) temperature sensor. See COOLANT (ENGINE) TEMPERATURE SENSOR in I - SYSTEM/COMP TEST article.
Check fuel level in tank.
Check for oil leaks into combustion chamber.