Well you can start by the obvious disconnected hose and if you don't find any loose fittings or loose hoses, then you have to pull off the black flex loom and look for cracks. Sometimes finding vac leaks are a pain in the butt. But if you are getting all these codes from a leak it's probably gonna be a big one. maybe even your intake manifold gasket is leaking. or the seal between the egr or throttle body. Vacuum leaks can come from alot of places. I know that doesn't help alot, but it's just a time consuming process. if you take a piece of like 1/2" tubing and put one end up to your ear and use the other to probe around fittings and hoses, you can usually hear a hiss. Or you can buy one of those mechanics stethescopes, but some cheap old rubber hose works about the same.