Ok everyone, now that I am back (and yes, i know I still have to change the pic) It's time for me to get down to business on the Mustang again. As most of you know it's an I6 Coupe. Rebuilt, still original exhaust which will be replaced in a couple of days. But I have been having some weird problem lately. If I get up to about 55+ and stay there for a little bit, all the sudden the car starts shooting smoke out of the tailpipe, almost like it's farting! Then suddenly it stops, and everythings fine again for about 10 min or so. I dunno what to do! Still runs fine, but shakes a little more, almost like the idle got turned down. Any suggestions?