Ok, I've got an off road BBK h-pipe. Installed the MIL elminators. Check engine light went off. Ran fine for about 4 months like that, but since this April, the check engine light will go off for a few days and come back on for a few months. Any ideas? Car is next to stock. I'm getting ready to buy a nitrous kit and want to get this problem out of the way before that.