Locate the EGR valve
Inspect the valve, vacuum lines, and electrical connector for damage
Check for stored trouble codes with an OBD-II scanner
Start the engine and let it reach operating temperature
Observe idle quality with the EGR valve closed
Apply vacuum to a vacuum-operated EGR valve with a hand vacuum pump
Watch for engine stumble, rough idle, or stall when the valve opens
Release vacuum and confirm the engine returns to normal idle
Test the EGR solenoid for proper vacuum control
Check the EGR valve diaphragm for leaks with a vacuum pump
Test the electrical resistance of an electronic EGR valve with a multimeter
Verify power, ground, and signal at the EGR connector
Command the EGR valve open and closed with a scan tool if supported
Remove the valve and inspect for carbon buildup or stuck movement
Clean the valve and passages if carbon deposits are present
Reinstall the valve and retest
Compare test results to manufacturer specifications