Initial Inspection and Diagnostic Overview

1. Verify vacuum hoses are properly routed and securely attached. Replace crimped, cracked, or broken hoses.
2. Check the EGR Valve for loose attaching bolts or damaged flange gasket.
3. Make any needed repairs and verify symptom still exists.
4. START engine and run until normal operating temperature is reached.
5. Disconnect the vacuum supply hose at the EGR Valve and check for a vacuum signal.
NOTE: The EVR solenoid has a constant internal leak, causing a small vacuum signal (less than 1") to be noticed at idle.
6. Connect a tachometer.
7. Verify idle speed is set to specifications with the transmission in NEUTRAL.
8. Disconnect the idle air bypass valve electrical connector.
9. Remove and plug the EGR Valve vacuum supply hose at the EGR Valve.
10. Using a hand vacuum pump, slowly apply 5-10 inches of vacuum to the EGR valve vacuum nipple.
11. When vacuum is applied to the EGR valve, the idle speed should drop more than 100 rpm or the engine should stall.
If not, check the EGR Valve for contamination and/or sticking. Check exhaust passages for blockage.
Clean valve and/or passages. Replace valve if necessary.
12. Reconnect the idle air bypass valve electrical connector. Reconnect the EGR vacuum supply hose.


DIAGNOSTIC AID: If a functional test of the EGR system is required as part of the emissions testing procedure, the EGR system can be checked by placing a "T" fitting in the vacuum line at the EGR valve, connecting a vacuum gauge to the fitting with a long hose, so that the gauge is visible while driving. Drive the vehicle at approximately 30 mph for a short distance. The EGR system should actuate the vacuum signal to the valve when the engine control system goes into closed loop operation. If the system does not actuate refer to COMPUTERIZED ENGINE CONTROLS/DIAGNOSIS AND TESTING for further test procedures.