I have a 98 dodge avenger 2.5 it act like it wants to die out at a stop sign or red light. It lacks power and when I turn on my head lights the RPM's drop. I took off some vacuum hoses checking for leaks then the RPM's go up.

Does it shudder or shake when it wants to die or does it silently turn off? If it shudders before it stalls its probably a fuel delivery problem. If the rpms drop to zero quietly then its an electrical problem. If your headlights are affecting your rpms make sure your battery terminals are clean and your ground is solid. Could also be your ignition switch wires going bad or ignition coil. Both require proffesional assistance. Pop your hood and do a general inspection making sure your fuses and plugs are completely secure. Make sure your throttle body is clean and check your idle air control valve for build up. If those are clean, have your throttle position sensor checked to make sure its working properly

You are almost there. The problem is a faulty idle air control valve IAC. This is a ECU controlled electrical device that allows air to by pass the the closed throttle plate when the engine is at idle. When you disconnected a vacuum line you introduced air into the inlet manifold effectively doing what the IAC should be doing. The IAC is located with the the throttle body. Remove the air ducting from the air cleaner to the throttle. Clean the throttle body interior if dirty ( a cloth dampened with WD40 or carb choke cleaner works well). There is a passage in front of the throttle plate that leads to the IAC. Make sure this is clean. Disconnect the IAC and unbolt it from the throttle and take care not to damage the gasket as you can reuse it when you reassemble. Make sure everything is spotlessly cleaned. The valve is a motor driven pintle, again this should be thoroughly cleaned and should be checked that it is free to move. When the IAC and the air passageways on the throttle are looking like new reassemble everything, remembering to reuse the gasket. Reconnect the electrical plug and that should the job done. If the problem persists check that the IAC motor is working. If not it will need replacing.