Exhaust Gas Recirculation: Testing and Inspection

Fig.14 - Checking EGR Valve Rod Movement:

The EGR valve operates on a vacuum signal from the throttle plate. With the engine idling, the valve must be closed (check by observing the rod movement through the observation window in the valve housing, Fig. 14). If the valve is open at idle, rough idle will result. Adjust the throttle stop screw to position the throttle butterfly so that the valve will be closed at idle. This can be checked by connecting a vacuum gauge to the vacuum line from the intake manifold to the EGR valve. With the throttle plate properly adjusted, there should be no vacuum gauge reading at idle.

1976-82 systems incorporate a thermostatic valve on certain models. This valve cuts off the vacuum signal to the EGR valve when the engine is cold.