Exhaust Gas Recirculation: Description and Operation

Fig. 144 EGR Components:

The EGR System controls the formation of NOx (oxides of nitrogen) emissions by recirculating some exhaust gases into the combustion chamber.
The EGR valve is controlled by the ECU through the EGR solenoid. Only when the following conditions are met does the ECU energize the solenoid which redirects vacuum from the source port and valve port to the source port and vent port preventing the EGR valve from operating:
^Engine starting.
^Engine speed over 2700 RPM.
^Low coolant temperature.
^High coolant temperature.
The amount of vacuum allowed to the EGR valve is directly dependant on the throttle valve opening and the amount of ported vacuum being generated at the time.