We had one that did this - rough slow idle, had to keep foot on brake and a little gas next to keep running, Once going, went okay. Service Engine light came on and idle would be worse. EGR valve was plugged up with carbon deposits. DH would remove valve, blow the carbon out with the compressor and it would be good for about 6 mo, then do again. He would clean again. Never did replace the valve - got rid of vehicle a couple years later and it was still running great with a cleaned out EGR valve. Ours must have been working properly when not carboned up.
