98 Windstar Stalling

My 98 Windstar recently began stalling when idling at redlights, stop signs etc. I heard a hissing and figured it was a vacuum leak. After replacing a hose that i believed to be the bad one, it now idles fine in park or in drive at redlights. It is now stalling while driving, letting off the gas to go around turns or when taking foot off the gas going down inclines. Any ideas?

Providing that you have solved the vaccum leak, the first thing to try would be the Idle Air Control valve (IAC).
It is mounted on the Upper intake manifold, next to the trottle body.
I would try cleaning it, using a spray lubricant like SeaFoam 'Deep Creep' or even WD-40.
You remove the 2 small bolts that hold the IAC in place, and hold it so that you can spray the lubricant in....and it will run out....so that you will be flushing away the dirt in there.
If this does not work, you may need to replace the IAC.
It is possible for the IAC to be sticking, and not result in a CEL.

The IAC is driven by the PCM and provides a additional way for air to enter the manifold in addition to the throttle plate that your accellerator is controlling.
This is how the PCM controls the engine speed when your foot is not on the accellerator.
It needs to be able to react quickly, or your engine can stumble or stall as you describe.

Thank you so much, I cleaned the IAC valve as you suggested and so far so good. Coming from a NON mechanically inclined female, if I could do it so can anyone else.

I think I jinxed myself by replying. It's stalling out again today. There is a hissing noise that I think is causing the vents to not open and close correctly and most of the time the heat is coming out the defrost. Could that be enough to cause all this stalling??

Yep, most likely. Since you're already like a beagle hot after a rabbit, you sound like you are on the right trail and be able to get yourself. You just have to figure out if it is inside the van or in the engine compartment, and then where exactly it's loose.

When a vacuum line is disconnected, it causes the engine to act like it's running out of breath and may stall. It also will affect whatever it is supposed to be connected to and that thing will not work. Since your hvac (heater vents, etc.) are vacuum operated as you wisely deduced yourself, they are not working as you observed and may related to the stalling.

As a matter of fact, you may even have noticed that when running the AC you will hear a strange popping noise every so often. It is a vacuum diaphram that is part of the ac control system.

A final thought, since you have had two leaky, disconnected vacuum lines, I am suspicious of the cause. Did someone recently work on it and disturb these lines? Or, are your lines breaking down, rotting and are no longer any good. If so, then you should consider replacing them so you won't have them plague you over and over. Good Luck!!!

If you hear the hissing sound more from inside the vehicle then it is likely one of the vaccum lines to the vaccum "motors" that drive the diverter doors that determine where the air goes.
With NO vaccum, all the air will go to the defrost.
When you look up under the dashboard, you will see some silver "bulbs" with the vaccum lines going to them.
It is pretty awkward getting a look up there, I have my legs outside the front door and my upper body on the floor, as I look up under the dashboard.

The TEMPERATURE control is NOT vaccum driven, it is a electric motor, and so it would not be relative to the problem you are having.

If you have the optional rear heater/Airconditoning unit, it has some vaccum controls, including vaccum to one of the switches on the dashboard.
I don't have the rear unit, so I am not personally familiar with it, but there are some posts about issues with vaccum controls for it.

If you here the hissing sound more from the engine compartment, the vaccum source is from one of the vaccum lines to the back side of the upper intake manifold.....passenger side.
That vaccum line goes to a black resevoir "box" that is mounted on the passenger side inner fender.
From that box, another vaccum line goes through the firewall, into the passenger compartment.
I just looked through my pictures and sadly I don't have one posted that shows the resevoir box that I am talking about....
But from the engine compartment, your best bet would be to find the vaccum resevoir box, on the inner fender, next to the the upright cannister with the metal A/C lines (which is the A/C accumulator, aka dryer) and follow each of the 2 vaccum lines that connet to it.

Hopefully your problem is just a vaccum line that has been bumped loose.
I have not seen posts indicating issues with the vaccum "motors" that drive the diverters, although they can be bought through FORD if need be.

Not exactly how I wanna spend my Thanksgiving. I think I found the "silver bulbs" you spoke of. Two on the driver side with each having two skinny colored lines attached and 1 under the passenger side with an orange one attached. None of which seemed to be loose. You're right, not easy to look at. Now on the step 2 to try and find the other lines you spoke of. The hissing sounds seems to come equally from inside and outside.

Vaccum leaks are tough to track down, mechanic or not.
At least you have a hissing sound to help, but it is still not easy.
I am wondering if perhaps it might be where the line passes through the firewall?

Found the black box you're talking about and the lines that come from it that go to the back of the manifold. Wiggling doesnt change anything (hissing sound), where exactly does it go thru a firewall. I see a start at the box and a stop in the back where it seems to go into something else. Im getting frustrated but not giving up. Hunting season is big around here (mechanics holiday) and last week of the month most garages are busy.

When I can't isolate the location of a noise coming from my car, I will sometimes use a piece of flexible tubing, a straight tube or pipe, a short piece of garden hose. obviously the louder you are, the closer you are. Another possibility is to disconnect vacuum lines upstream of your leak, then keep tracking closer and closer to your leak. Good luck