1975-76 912E & 914 Models

With engine idling, allow by-pass line between muffler and EGR valve to become hot. Increase engine speed to 4200 RPM. Exhaust gas line between EGR valve and intake system must now become hot also. If not, check for defective EGR valve, plugged EGR or vacuum lines, or for plugged vacuum bore in throttle valve housing.