You don't give a lot of extra information. The missing hose could cause a vacuum leak, which would definitely make it idle like poo. Start by blocking it off to see if that improves it.
You mention high CO which sounds like you have recently had a state-mandated emissions inspection and failed. If that is the case, what state? If you have high CO while testing on a dyno at 15 or 25 mph, then don't bother with the idle mixture. It only controls the mixture at idle. As soon as you get going, it stops doing anything. High CO can be caused by a number of things, including a dirty carb. I would start with a tank of premium gas and a bottle of injector cleaner like Techron or the like. You can also buy carb cleaner in a spray can. Other potential causes include: dirty air filter, sticky choke, malfunctioning PCV, bad charcoal canister or a misadjusted carb (probably needing a complete rebuild). Good luck and keep us posted.