Non-Turbo Models
System uses 2 throttle edge vacuum ports to modulate EGR valve opening. When throttle is closed, both outlets are subjected to atmospheric pressure and no vacuum is obtained. When throttle is open slightly, vacuum is present at 1 port and opens EGR valve part way. As throttle is opened further, both ports have vacuum and EGR valve is opened fully. Thermal vacuum switch prevents EGR operation below a coolant temperature of 113°F(45°C).