Code P0455 along with 171/174 Help please

[SlimJimRD]

I have a 99 Winstar with 3.8L engine 110,000 miles.
A little over a year ago (98,000 miles) I had a coolant leak in the cross over pipe. Because I had to take off the intake to replace the pipe I went ahead and did the isolator bolts etc to hopefully prevent the 171/174 issue. I also replaced the plugs, wires and all coolant hoses while the cowl was off.
I did not change the valve cover as it did not look like it was leaking and seemed to be easy enough to replace later.
Well now I have the 171/174 code along with P0455 (EVAP large leak detected).
I cannot find any leak. I also cleaned the Mass Air Flow sensor to see if that would help. So far no luck.
Any ideas how to find the problem with the P0455? Is it possible related to the 171/174?
Do I need to redo the 171/174 isolator bolts etc because of the code or could there be other causes of these codes?
Thanks
Steve

[12Ounce]

I wonder if you just plugged the EVAP system right where it starts at the manifold ... and see if the 171/174 codes eventually go away. That would indicate the EVAP is the problem.

[SlimJimRD]

I see I never finalized what happened.

I erased the code and it never came back.