'98 Ranger EVP sensor melted

My check engine light came on. About that same time I heard a strange noise under the hood. I found that it came from a tiny motor on the top of the intake (this ran intermittenly). After further inspection I notice that the input port to my EVP was melted. The check engine light shows auxillary emission control. I replaced the EVP and cleared the check engine light. After over 200 miles, the check engine light came on again, and again the EVP was melted. Does anyone have any idea why the EVP keeps melting? HELP!!!!!!!