800 rpm is the correct idle. Is yours below that? Rough idle could be caused by a few things. Also, if you have an automatic, that is why it is sluggish at first. If not, it still wont make much power until you hit around 3k rpm.
<span style='color:gray'><span style='font-family:Courier'>1995 e36 3 Series RIP
1999 e46 3 Series BURN IN HELL
2000 MR-S Roadster= Current</span></span>