99 windstar 3.8L Rough idle & accel misfire

I have a 1999 Windstar with a 3.8L engine. The van has a rough idle only when in drive or reverse and when accelerating on slight inclines I get what feels like a backfire or misfire. I replaced the spark plugs and wires about 10K miles back with E3.64 plugs, rather than stock motorocraft plugs, and OEM wire set. At the time of replacement and for a good 6K miles there was no issue, MPG increased and car ran very well. But now I have this consistent problem, and it did throw P0401 and P0171 codes. I've had the car to a dealership who suggest I had a vacuum leak with the upper intake crossover. So I order those parts and sure enough the EGR ports were dirty and it looked like one of the intake gaskets were leaking. Although it seemed to help slightly the rough idle and misfires continued after completion of that job.

Further research suggested the DPFE might need replacing and when I back probed the VREF lead with engine on motor off there was 12V where there should have been .2-.4. So I thought I'd order a DPFE, since mine was the original and after 10 years it probable needed replacement anyway. But I'm still getting the rough idle and acceleration misfire. The dealer also suggest only using motorcraft plugs, I assume because of the double platinum finishes. I'm checking on the electrode and ground wire base metal of the E3 plugs.

I've also checked the voltage and cleaned and confirmed the Idle Air Controller is working (which shouldn't affect acceleration) and I've cleaned but not back probed the Mass Air Flow sensor.

Any thought of where to look next would be appreciated. One thing I plan to do is to pull all six plugs and check on their conditions today versus when installed.

Thanks for any help and suggestions.

sounds like you've covered your bases pretty well. I do know that lots of people have had problems with non-OEM plugs. For the cost and ease of install, I'd be doing that first.

Piper

I also think you should change your spark plugs to oem motorcraft or autolight plugs as other spark plugs have caused misfires. I would also clean out the Idle air control and also check your ignition coil for cracks as that might need to be replaced as well. http://www.leckemby.net/windstar/windstar02.html
http://www.leckemby.net/windstar/windstar01.html

One other thing to check (and the above suggestions should be checked out) is the IMRC links.....on your year...it is not unusual for the nylon clips that connect the IMRC shafts to the electrical actuator motor to become disconnected.
If only 1 is missing....then you end up with an unballanced condition between the front and rear bank of cylinders.....and the PCM cannot deal with that.
If both are disconnected.....you could have the IMRC open when it should not be.
On your year.....the actuator motor is doing its thing....and the sensor is a part of the actuator motor....so the PCM thinks that the IMRC is moving when it is not.

The IMRC is located on the passenger side....on the lower intake manifold......there are shafts that pass through each of the front and the rear bank of intakes.....and they open an extra port for air to flow in under high accelleration conditions.
Under normal driving....they are closed......

Thank you to all. I was aware of the IAC cleaning issue and also the note to clean it, that was the first step before I cleaned the EGR ports per the links in the this thread. I will have to get some new plugs to replace the E3's. I have checked the IMRC bushings and that was an issue, now corrected. I'm not convinced the plugs are necessarily the issue, because there is one other symptoms that I've identified since. First, the missing only seems to occur after between 2 and 4 minutes of running from cold. Second, the motor, after warming, doesn't want to rev above about 3400 RPM, it starts to lug like it is starving for fuel. I'm wondering if anyone might have an idea of what the PCM does based on time elapse after motor start-up? And I'm wondering if a low fuel pressure would cause symptoms like this? I have checked the pressure regulator for fuel in the vacuum line and their is none.

Thanks again for ideas of where to look. Best Regards, Brian A