Vehicle is running rich, Hard start, runs rough at idle.

I have replaced maf sensor, new plugs, new wires, new cap and rotor, new iac valve, and egr. Only code it continuously throws is p0401 egr insufficient flow. it sometimes will throw a knock sensor code and at one point it threw a code for system to rich but the codes cleared by themselves. How could the coolant temp sensor cause this issue and if it were to malfunction the sensor wouldnt it throw a code? This really has me puzzled. Someone told me it could be the fuel pressure regulator failing do you think that is possible?

I will be anxious to see what the answer is to this question for I have the same problem with mine. Starts right up when cold, hard start after driving for a couple minutes. I also have been told it is the regulator/ spider injection system.