Ok heres the problem... my 4.9 starts ok but idles at about 500-600 rpms when it first starts up. sometimes it may even stall out. however once i rev it up a few times the idle starts to grow closer to 800 then about after 15-20 min of driving all is well. any ideas on what may be causeing the problem. Also the idle is set for 900 rpms yet despite that it idles lower and black smoke fires out the back when you rev it in that condition.
