What happens if the egr valve doesn't work at all? What does it do and whatnot?

 

Introduces small amounts of exhaust gases into the fuel mixture, reduces cylinder temperatures, and decreases nox emissions.
That doesn't mean that it'll run hotter because the cooling system can handle the extra heat, but at idle the thermostat may stay open longer.

 

EGR is not open during idle, so it's operation has nothing to do with the temp during idle.

EGR is only enabled when you're going over 35 (I believe) and when you've been cruising at low throttle ( some percentage i forget) for a certain amount of time. The DIY Prom guys know the specifics.

 

You're right I forgot about that, been up all night replacing the nose, reinforcement, and left fender. That frontend has a boat load of screws, and bolts. The headlights were a pain.