Dodge Dart carb tuning issues.

Hey guys!

Today a friend and I tried to tune my Dart. The car always idles pretty high and we decided to tackle that today. Yesterday, I took the car out for a spin, but when it was stopped at a light, it would shake rather violently and i would have to give it gas for it not to stall. One problem with it, the idle speed screw doesn't really work...It can increase the idle more but when we loosen it all the way out, the idle stays pretty high. I have no idea what the RPMs are since there is no tach :banghead: . We tried to adjust the mixture screws and we had no idea if it was enough or not... Were only 18 and kinda noobs about this lol. If i get a vacuum gauge, how should I hook it up? The car has a 650 Holley and a Edelbrock performer manifold. My first priority is to adjust the idle speed though...The former owner mentioned that it might need a new throttle cable soon though. My friend got in the car and hit the gas all the way down and the butterflies were perpendicular to the manifold. I tightened down the carb to the manifold and checked for leaks from lines going to the carburetor. What else could cause this to happen? Anybody have any idea how to effectively tune it and check for vacuum leaks? Sorry for the super noob question but im just starting out :).