I'm still trying to track down the source of my P0401 that keeps coming back. I've replaced the EGR valve, DPFE sensor, DPFE hoses, and EPR solenoid. It still idles rough at times and when coming to a stop. Driving is fine. I've verified the DPFEV PID values is correct while running and off. I checked vacuum hoses for pinches or breaks and there was none. When the EGR valve was off I cleaned the port but there wasn't anything really to clean or in the EGR tube. The only part I did not take off was the tube at the exhaust manifold because I figured it might be difficult or strip threads. When the engine is loping, missing, running rough at idle and I unplug the EGR valve vacuum hose it immediately runs smooth and even. What's going on there? Does it point to anything? I'm going to try and get my muffler and tailpipe replaced tomorrow because the baffle inside is broken but I don't think that will cause the rough idle, since it smoothed out perfectly with the EGR vacuum unplugged.

 

Did you plug the vacuum line when you disconnected it from the EGR? You are admitting more air to the intake if you did not.
I would attach a vacuum gauge to the EGR vacuum line to see if the control valves are leaking vacuum(which opens the EGR) at idle. They could be slowly 'seeping' and the diaphragm will slowly lift the EGR valve off its seat, even at idle, if the vacuum builds enough.
You can get a muffler from Advance that is a fit for the 2.3. The one I got was also spec'd for a 302 Maverick, so I figure it could handle 1/2 that displacement with no problem. The tailpipe is a less-than-$20 part if ordered, and is pretty easy to install. Hardest two things were snaking over the rear axle, and pushing the hangers into the rubber donut thingies. Or you can spend more bucks at a muffler shop. I just remembered there's a Meinke here in Canton, as I was thinking I did not know of one local.
tom

 

I had the egr hose off the egr valve just plugged with my finger at idle and I didn't feel any vacuum. But I know when we disconnected it ran smoother. We also disconnected the vacuum lines at the epr solenoid and it smoothed out too. I replaced that part with a Dorman one. We thought maybe it was bad. So I swapped back my old epr solenoid and it ran smooth the whole day I drove it. I even drove to the muffler shop and had the muffler and tailpipe installed. It ran so much smoother. However, on the way home, probably round trip 25 miles CEL popped back with P0401 again. I didn't feel any idle roughness except when heavy braking to stop. However, when I got home I shut it off came back inside and got my laptop with the FORSCAN on it. When I started it back up after it had only been sitting 5-6 minutes the rough idle in PARK was back. I checked the DPFEV PID and it was pretty steady at KOEO around .40. I drove it around the neighborhood and got it up to the 30MPH and compared to the Fords PID values for a 98 Ranger 2.5 Auto. The range at 30MPH was like .20-4.5. Mine stayed mostly around .38, .40. .42. So I assumed the DPFE is working right. But something is not right. I did notice the area around my PCV valve is greasy and dirty. I don't know if that would have anything to do with an intermittent P0401. I unfortunately don't have a vacuum pump to test the valve by hand. I saw a youtube video where a mechanic took off the epr cap and plugged the whole to see if it would stall. I believe he said if it does that then the egr system is free of blockages. It's rather annoying I've never even had a P0401 code on this truck until now.