2000 Windstar runs rough/Check Engine

My 2000 Windstar 3.8 L started running rough about 10 days ago (it seemed to coincide with weather jumping into the upper 90's). We've obviously been using Max A/C during the hot spell. About 3 days ago, the Check Engine light came on and stayed on until yesterday. It continues to run rough on occasion. I replaced the DPFE sensor about 2 years ago. Any ideas as to what might cause this issue?

Thanks

Yep, several hundred ideas perhaps.

We can narrow it down to a couple if you get the code.

You can get your codes read for FREE at many auto parts stores.....if you live in the USA.
When you do this....make sure that you get the actual numeric code......such as P0301.

Their display will give a numeric code, and a brief description.....they often just tell you the description, as most people don't know what to do with the numeric description..
They may simplify it further by just saying "misfire"......and P0301 IS a misfire.....but is a misfire on cylinder #1.

YOU DO KNOW what to do with the code.......come back to this forum, do a search on the numeric code.......and / or post the code.
Almost certain someone else has had the code (lots of people.....with windstars = lots of experience).

Be wary of the auto part store clerk's advice......especially if they advise you to buy new oxygen sensors....as oxygen sensors are NOT a high failure item on the windstar.

P0401, P0301, P0304 are often codes that have to do with clogged EGR ports in the lower intake manifold. You can get 1 or more of these codes for this concern. My case, it was P0304.

DPFE is a high failure item......but check the 2 rubber hoses that go from the DPFE to the EGR pipe (runs from the EGR valve to the front exhaust manifold.
Also check the vaccum line connections from the EGR valve, to the EGR vaccum regulator solenoid (on the upper intake manifold on my '96), and the vaccum line from the EGR vaccum regulator solenoid to the vaccum source.
The EGR valve is NOT a high failure item.

If it is a code P0171 and / or P0174.....it is almost CERTAIN that it is NOT a defective oxygen sensor. Your 2000 has a TSB (Technical Service Buletin) and there is a great website that explains what you need to do or have done.
These codes are the most often cases where people are sold new oxygen sensors.......which they do not need.
These codes are almost ALWAYS the result of a vaccum leak.

Sorry for the long post....trying to help prevent you from spending money needlessly.

Thanks for the info. The code is P0306 (6 Misfire Detected). The light is now off. I also noticed that with the car in neutral it coughs and sputters above 4000 rpms. This Windstar has had a variety of issues already (new tranny, replaced DPFE sensor, etc) so I'm no longer surprised!

Thanks in advance for any help.

I can speak for the "misfire" in park above 4000 rpm. When I did my first maintenacne on mine 4 years ago, (replacing a fuel pump), I discovered that too and fretted until I talked to a Ford servicewriter who told me it was simply a rev-limiter that kicks in at 4000 when not in drive. I asked him how to get around it if testing is needed, and he said all they do is put it in gear up on the lift!

Anyway, I don't know why you are getting a misfire on #6, but that's why it cuts out in neutral or park. Start with the spark plug. Have a look and test if you are getting spark first, then look at the condition of the plug. The plug will tell you if it's been burning anything addtionally with the fuel. BTW, check your coolant level. If you are using coolant, you might be dealing with a gasket leak (intake manifold or possibly cylinder head). But, there are steps to take to narrow this down soooo let's not jump to conclusions.... ( I just happen to be doing my intake manifold tonight on my 98 -It's been drinking coolant lately, blowing white smoke which reeks of glycol, and misfiring on #4.) Also, check your dipstick, pcv vent tube, and oil filler cap for signs of coolant in the crankcase (it will resemble chocolate milk shake). The presence of coolant in the crankcase would indicate a gasket failure and you would need to PARK IT NOW, so as to not destroy the bearings and piston rings. Anyway, maybe it's just a bad plug wire or plug - start there.

HTH

Another item could be the EGR ports. If # 6 is clear and some of the others are blocked or excessive then there may be too much EGR flow at cylinder #6causing a misfire. (I am unsure of which cylinder(s) are more prone to this problem) The EGR systems also kicks in at higher RPMS. You can try disconnecting the vacuum control to the EGR valve (and block the end of the hose with a golf tee or something similar). If this eliminates the problem then the EGR port is the thing you should chase further. This EGR disconnect may temporarilly through a code but the misfire should cause the CEL to flash.