1974-84 (Ported EGR Valve)

With engine at normal operating temperature, raise engine speed 3000-3200 RPM. Disconnect vacuum hose to EGR valve. EGR diaphragm should lower. Reconnect vacuum hose to EGR valve. EGR diaphragm should rise. Allow engine to idle. Disconnected vacuum hose to EGR valve and plug hose. Apply vacuum to EGR valve. Engine idle speed should become unstable or stall. If EGR valve operates as indicated, EGR system is functioning properly.