started getting a rough start after the engine has cooled down. sounds like fluttering or chattering, idles all over the place. after a few seconds it maintains its high idle for warming up. not getting any check engine lights yet. 6600 miles on truck now. been looking on ramforumz, pretty good sized post about this there. no definite answer though, 91 octane, air filter, ambient air sensor and goes away on its own seems to be the main answers.