My car had the code P0401 came on once and disappear. The car is
running fine but idle is very rough and stall at the stop light. I did change the DPFE sensor but it won't help. Please help...Thanks.

http://www.obd-codes.com/trouble_codes/generic/p0401-insufficient-exhaust-gas-recirculation-flow-egr.php

Check into that. It sounds more like a lot of water in the gas. My sister's Taurus would not idle, but it would run at higher RMPs fine. I just had to mantain the gas pedal right, come to find out someone put water in her tank. We put a full tank of gas and a couple of bottles of dry gas in and it came around in two days. Hope that might be it, or other wise check the EGR system for plug-ups.