[Torquer]

if i had a vacuum line i didnt know where it went i would at least plug it up with something, so you dont loose vacuum pressure. If there is a vacuum hose on it try to see where it reaches to, but if no line then um i dont know, try to get a diagram for your engine. i had a vacuum line on my old car that I found a screw that threaded into it perfectly.

for a rough idle maybe check the IAC plate area, make sure its well cleaned. make sure the IAC plate isnt sticking, usually does this in temperature extremes hot or cold. Then maybe check the TPS sensor, controls fuel. But this usually only affects idle and not so much when you get going. usually goes more on MAP and MAF sensors at driving speed

if its a weird looping idle, could be the MAF sensor or the o2 sensor.

If the engine runs rough at High or low speeds but fine in between. might be emissions sensors like EGR, EVAP, or PCV.

oh yeah and dont forget to check the air ductwork, that could caus an idle problem too. With some of the sensors to test them just unplug them before you start up the truck. The computer has a stored idle code in it if one of the sensors is unplugged it will just use the default code. so if the engine runs better without the sensor than you know where the problem is. this doesnt work on all vehicles though, some wont start with a sensor unplugged. and dont unplugg it with the engine running, that will usually give you a trouble code and a check engine light.