The ECM controls vacuum to the EGR valve electronically--through the EGR bleed solenoid.
When the engine is warm the solenoid is de-energized allowing vacuum to the EGR valve.
When the engine is cold the solenoid is energized blocking vacuum to the EGR valve.
The solenoid also decreases the amount of vacuum to the EGR valve when the torque converter clutch is engaged.