Nissan Repair: 95 nissan altima wont shift into fourth gear, nissan altima, vacuum line

Question
Car shifts smooth into 2nd and 3rd gear. will not go into 4th. I have changed the speed sensor, although every once in awhile, you lose the speedometer, then it suddenly comes back. I have changed the fluid and filter.  
Also, there is what looks to be a vacuum line, located along side of the air cleaner. It is an open line and is not attached to anything. Do you know where this goes and could this be a problem? Thank you for any help you can give me

Answer
Paul,

Seems like you might have found the problem.  You see, the transmission will not shift into fourth without the engine being at operating temperature and the vacuum sensor reading that the car is not under load.  Then, it will shift into fourth and the converter will lock.  Other causes for this is a bad vacuum sensor or the valve body in the transmission itself.