Started up the 99 Ex 4.0 this morning, It was running rich and stmbling for about 5 minutes then it seemed fine. Took it out on the highway to blow the gunk out of it for about 10 miles @ 55mph, came back into town driving around and check engine light came on and stayed on. Came home disconnected the battery and her cool down, connected battery back up after a couple hours started it up same problem stumbling and burnig rich again for about 5 min. out on the highway I go come back into town, check engine light came on again. anybody know what is wrong?