Ive had a somewhat rough idle throughout my ownership of a 780 ti (same engine). I recently replaced the rear main seal, and in doing so replaced the distributor. In doing so, I also removed the distributor and was forced to reset the timing and idle. My engine has been running much more smoothly lately, something which I attribute to my adjustment of the timing (I cant tell you the original timing spec because I didnt test it first). If you look at the procedure for setting timing in any manual, it also recommends adjusting idle at the same time, this allows you to sort of "hone" in on the ideal 12.5 deg BTC/750 rpm. Also, since I live in houston I set the idle while running the AC, since I really use it as a non-optional accessory.