I recently picked up a 78 280z. On startup the RPMs jump to 2000, I've replaced the throttle body and reinstalled the AAR since someone previously deleted it. No changes. The EGR has also been deleted. Any ideas would be helpful.

 

You are getting extra air in somewhere. Is the AAR functional? Test it by warming up the engine and pinching the hose on the inlet side of it to see if the idle changes. There should be an idle adjustment on the throttle body, have you messed with it? Try pinching the hose to the brake booster too. Nice radiator! Ugly intake boot. Check out my post on another zcar site about optional air meter boots.
Air intake boot options