I have a 2000 Maxima with a problem with erratic idle and cut off when
cold.  When you crank it up in the morning it starts to idle at about
1300 rpm then drops idle and cuts off.  If I try to press the gas pedal
and rev the engine it may or may not cut off.  Once I get it going it
cranks fine the rest of the day even if it sets up until 5 pm or later.
No problems unless it sets up over night.  I took it to the dealer and
they replaced a sensor at the back of the car, but it did not fix it.
No codes.  Had other mechanics look at it.  One replaced the fuel
filter.  Still did not fix it.

I was looking this morning at the engine and found what looks like a
vacuum hose next to the measuring stick for the transmission that was
not connected to anything (right behind the air intake from the grill).
It comes up along the measuring stick and has a thicker tube that
comes up and then down.  I can not see where it should be connected to
anything.  Could someone tell me what this is and if it should be
connected to something?  I wonder if this is my problem?

Any help would be appreciated.