After Warm-Up

Check EGR control valve operation.
Perform power balance test.
Perform appropriate test in INJECTOR MALFUNCTION diagnostic chart in I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section. Use DIAGNOSTIC CHARTS DIRECTORY table in I - SYS/COMP TESTS article to locate chart.
Check for spark using spark tester.
Check spark plug for improper gap or fouling.
Ensure fuel pressure is within specification.
Disconnect exhaust gas sensor and monitor change in driveability. If it improves, replace sensor. If not, go to 16.
Ensure there are no vacuum leaks into intake system.
Inspect throttle body ports and valves for deposits, wear or plugging. Clean or replace as necessary.
Ensure engine has adequate compression.
Check ECU harness connector.
Try a known good ECU.