Suspected Vacuum Leak

Sorry if this get a little long. I would just like to explain what is happening and try to find a real solution.
I have an 88 XJ 4.0 with AW4 and 231 tcase. I have only owned this jeep for 3 months. When I fist bought it I was actually impressed with its power (acceleration). If you pressed the gas on the XJ it would really take off. Well times have changed. It feels VERY sluggish now. It even stubbles if you accelerate to quickly.
I replaced the spark plugs, wires, cap, rotor, fuel filter and air filter. None of this has helped the problem.
I now have a new symptom also. My part time light on the dash comes off and on. It only comes on when I am coasting. Like when I am coming down a steep hill and let my foot completely off the accelerator. As soon as I begin to press the accelerator again the light immediatly goes off. The only exception is that if I am coasting to a stop and I press the brake pedal. The part time light will stay on until I release the brake and press the gas.
Today I spent a good 2 hours looking for a vacuum leak. All I could find is a Blue vacuum hose that comes from the harness that is connected to the hard lines from the transfercase, Disconnected. It is with a group of vacuum lines that run against the passenger side fire wall, under all the a/c lines, along the fender and down to the resovior bottle behind the bumper.
Is this BLUE vacuum line supposed to be connected?
If so where? I could not find any place to connect it.
I really hope someone our there can desifer all this rambleing and help me find a solution to my problem. I really need to bring the power level back up to there it was!

Thanks in advance for any help!!!
Jason

The blue vacuum line seems to be a vent to outside air.
As for your power problem......probably nothing to do with the blue vacuum line.
Clogged exhaust???? You may try loosening the exhaust pipe at the bottom of the manifold and see if the power returns. It will be very loud but might provide an answer
Hope this helps

Later

Phil

If you suspect a vac leak you can find it by spraying carb cleaner around the lines, when you hit the vac leak you will hear the idle change. Big one is the hose that runs under the battery to the vacumn cannister in the front bumper, passenger side. Yes, it is INSIDE the front bumper. Also at that age all those vac lines could be aging poorly and devleoping cracks. If you use the spray method and find a bunch of areas it does this in go park at a parts store and start swapping. I had to do that with an 89YJ two summers ago. What a PIA that was...

OK here a little update. Maybe someone can still help me.
I have check ALL my vacuum lines and they all check out good. The part time light now stays on all the time. So I have changed something! I have noticed that if I unplug the red vacuum line, and only the red vacuum line the light will go off. The problem is I can't find anything in between this vacuum line and the transfer case to go bad. It runs from the storage canister straight to the transfer case.
My question now is...is this red vacuum line suposed to have vacuum on all the time? If not that is my problem. What is suposed to cut the vacuum off to this line, if it is suposed to be off?

Thanks,
Jason

The first pic is when it is in 2wd mode. The second pic is when it is in 4wd
As you can see the RED line has vacuum on it all the time. Vacuum comes from the engine to the tank then to the red line and so on........