[wiswind]

I tried to look on the Autozone website....under repair guides...but they do not list the '99 windstar.
I looked up the '96 3.0L and the EGR valve is located under the throttle body. The DPFE sensor is located kinda right over the EGR valve.
The DPFE is MUCH higher failure as far as items failing.....however.....as you had work done.....I would check to make sure that there is not a vaccum line that has been bumped loose.

Using my '96 3.8L as a reference point....the EGR valve is opened by a vaccum....which comes into the top of the EGR valve through a hose. That hose goes to the EGR Vaccum Modulator Solonoid.
The EGR Vaccum Solonoid has an electrical connection.....and 2 vaccum lines. One vaccum line is the one that goes to the EGR valve....and the other is a constant (as long as the engine is running) source of vaccum. On my engine....that source.....ultimately....through a few "T" connections......is from the PCV line.


The Electrical connection on the EGR vaccum Solonoid.....ends up going to the PCM. The PCM gets a signal from the DPFE as to how much EGR flow there is.....and sends the signal to open / close the EGR valve. The EGR valve is not a high failure item....but as I mentioned....a problem in the vaccum connections is possible.
There is a pipe that goes from the EGR valve.....to one of the exhaust manifolds. This is where the exhaust flows from the exhaust manifold.....through the EGR valve....into the intake manifold.....

The DPFE has 2 hoses that go to the EGR Pipe. There is a slight restriction in the EGR pipe in between the the 2 hose connections....so when there is flow through the EGR pipe.....there will be a pressure drop between the 2 hoses....which will be an indication of how much flow there is in the pipe. The DPFE sensor....senses the difference in pressure....and converts that into an electrical signal...that goes to the PCM....and so on.

Sitting at idle....there should be NO EGR flow.
If you were to apply a vaccum to the EGR valve.....with the engine at idle.....it should start to run rough.....If it does NOT.....then there is a problem. I am not sure if the 3.0L has multiple EGR ports......or if it only has 1 port.... On the 3.8L....which has a port for each cylinder....the EGR ports often become clogged.

Sorry for the lengthly discussion.
I find it easier to solve a problem when I understand how the system works. Most of the windstars have the 3.8L engine......

You may find the autozone website helpful....even if you do have to look at 98 and before.....they have pictures and drawings showing where things are....and what they look like......