I purchased this truck a week ago. It was reading misfire in cylinder 4, PO443 evaporative emission control sytem purge control circuit, and another code(cant remember). I changed the coil and misfire went away along with the other code I dont remember. I still have po443, I was thinking of changing the purge valve. I have done a little reading online and have seen that this is not the problem, because its electrical. Can anyone help me. What steps do I need to take to find what is not working properly?