Idle problems and stalling.

[Mindgrip]

Hey there,
I have a 2002 S40. The vehicle started having issues with lag when I hit the accelerator. Now the car idles very rough and tends to stall while in park. I took it to a mechanic and the following codes were found...
P0171: System too lean (Bank 1)
P0420: Catalyst below threshold (Bank 1)
P0456: Evap Small Leak
P0101: Mass or Volume Air Flow Range/Performance
P0128: Coolant Temp. Bellow Temp.
P0301 thru P0304: Cyl. Misfire.

I have replaced the Mass Air Flow Sensor, Spark Plugs, Spark Plug Wires, and Thermostat. The lagging accelerator problem seems to have be solved with replacing the Mass Air Flow Sensor. The vehicle still idles VERY rough and will stall frequently. Any idea's on what could be causing this?