Thought I had this fixed. I've got a 2001 Expedition 84,000 miles with 4.6L engine. I've had this check engine light and the problems of a rough idle and poor acceleration for a couple of months now. I've been putting off doing the repair. Went to AutoZone and they told me P1401/Emissions. Stopped at the Dealership and they told me to replace the Coil Packs on #4 and #6 Cylinders (and all the others too!). Because I didn't pay for the scan they didn't give me the report. I went ahead and changed the plugs and coil on springs on all cylinders. I also changed the DPFE Sensor. The last time I changed my plugs about a year and a half ago I used Autolite... Well they still looked great-all identical wear. Wouldn't a rough idle and poor acceleration, if it was a spark related problem, show up on my spark plugs? Anyway, after changing plugs/boots/springs and DPFE the car ran fine for 50 miles or so and then the light came on again. Got the same rough idle back and poor acceleration. Once again my P1401 error code. By the way, it was only one code... I checked several times. I'm thinking that my plugs and boots and springs were fine and the DPFE also. It looks like I have a problem with one or more of my sensors that control the fuel/air mixture. Resetting the system helps until the sensors detect a problem and adjust the mixture (which takes about 50 miles). I read in a different post that a P1401 code can be caused by the following:

EGR (Bad Sensor/Connection/Wiring)
Evap System (Bad Fuel Cap,Saturated Evap Canister,Bad Vent Solenoid)
DPFE Sensor (Been There, Done That!)
Sub Throttle Sensor (Wires/Connection)
DMTL Module (Bad Module/Wires/Connection)
Fuel Tank Pressure Solenoid (Solenoid/Wires/Connection)
Intake Manifold (Blockage)

Let's assume that I have or will check for bad wires and connections. Anyone know how to diagnose this without changing all of these sensors one by one? Gas cap was not the problem... already done that.