Found a possible culprit to my idle issues, how do i fix it?

[Kdubslugga]

My idle issue is, everytime i start the car cold it dies unless i give it gas. This lasts for 3 min or so then its fine. Ive searched the idle sticky thread and still no go. Heres the thing, since i bought the car 3 years ago its had this problem. Now today i went out looking for vac lines and stuff because that has to be the problem because ive double checked everything else. Now on that vac port thing thats on the passenger side firewall, "the thing with 3 ports, 2 pointing down and 1 pointing to the drivers side fender" it has a vac cap on it on the one pointing to the drivers side fender. I ran a vac hose from that to the vac port thing labeled "A/C" and now when i turn the car off i hear a loud hissing coming from the ac vents right about the radio, what would cause this and how should i fix it? I really hope this makes sense!!

 

[Bottomlesspit]

I assume that the little vac cap has been on your car since you bought it? Did your HVAC controls all work? All positions on the dial?
The vac line you ran today is the normal setup...line from the left side of vac valve to the AC line on the vac tree.
Hearing the noise after you shut off the car leads me to think that one or more of your vac connections behind/under the dash is disconnected. You really only should hear that hissing sound when you switch the HVAC control knob between different dial settings...like AC to OFF position.
You should probably check the vac lines behind the glove box and up behind the dash on either side of the center console. The lines are brightly colored like yellow, red, blue, and a couple black.
Since the vac line to the interior controls was capped off I wouldn't think it would be effecting your idle, but stranger things have occured.
Hope this gives you a start on where to look, that's all I can think of right now.
Ken