I have a 98 ford windstar with a 3.8, that has an engine miss and two dtc's po401 and po402, would a bad EGR valve cause this miss?

Great...

egr... po401

Look at
1996 FORD WINDSTAR 3 8L V6 EGR Pressure Feedback DPFE Sensor RockAuto

Perhaps... (how's that for mind reading?)

Carnac the Magnificent

171 is a HEGO sensor unable to switch/ 174 is for HEGO sensor also.. 401 is insufficient EGR flow!! egr valve may be clogged or need replaced!!

PO401 is a egr problem, low /no flow detected. Unfortunatly most of the time with the 3.8 engine is the ports in the intake manifold get clogged. So if testing reveles the egr valve is working and the dpfe sensor is reading between around .8 to 1.2 volts at idle your probably looking at taking all the plastic plenum parts off to clean the passages. This can be done without removing the wiper box abobe the plenum but you have to remove the iac and sneek the manifold our from the drivers side forward first.

PO401: EGR insufficient flow detected
PO402: EGR excessive flow detected

A code P0402 most likely means one or more of the following has happened:

The DPFE (differential pressure) sensor is faulty and needs to be replaced
There is a blockage in the EGR (most likely carbon buildup)
The EGR valve is faulty
The EGR valve may not be opening due to a lack of vaccuum

I believe this code is insufficient EGR flow. On this engine, the passages to the EGR valve often become carboned up and cause this code. Remove the EGR valve and inspect the passages to see if they need to be cleaned.

Does the egr vavle open ? You will need to use a scanner to test the dpfe voltage when the egr valve is energized you should read around 3.5 4.00 volts. Also you could remove the vacume line from the egr valve and with the engine running you should see around 100 rpm drop in engine rpm at least this would indicate the egr valve is capable of flowing egr gases through the system to the cylinders.

po300 random/multiple cylinder misfire detected po301 cylinder 1misfire detected po401egr flow insufficient po 402egr flow excessive

I replaced the coil pack on my friends wind star when they had a mis. If you take the sparkplug wires loose and just set them on the plugs loose it will be easy to remove them with the engine running. Useing plastic plyers or some kind of insulated grabers, one by one take the wire away from the plug/or coil and see if it makes a difference.Take it away then put it back then go to the next one.If it runs the same when the wire is off then you probably will not hear a spark at that wire. The coils do go bad on alot of newer cars.
I hope this info helps you.

po401 is egr flow insufficiant ( the egr needs removed and cleaned also clean where it mounts to engine. po340 is camshaft position sensor A- bank 1 curcuit malfunction. it is a bad camshaft sensor.

I know this is a old post, but I had the same problem and it was the dpfe sensor. The EGR is almost never the problem with this code