Last weekend I noticed that my '03 5.4L started up a bit rough after sitting all night. It happened a couple of more times during the week. The truck sat all weekend and wasn't driven but when I got in the truck this morning the thing nearly shook my exhaust off. I've got a single in dual out flowmaster with the pipes straight out the back on either side of my hitch and it shook so hard the passenger side pipe was banging against my hitch. It will idle rough for 15-20 seconds then it settles down and drives fine under all acceleration. No hesitation whatever. I also have an AEM air filter. The exhaust and the air filter are the only mods. Any suggestions?

Edit* - Forgot to mention that I have 37k miles.

 

sounds like ur common cold start... ushould hook up ur block heater see if that helps any