did you buy it new? did you purchase from infiniti?
do you have an obd scanner? try to see if any codes exist to give you a start.
just so i understand, the car idles high as if you just turned it on for about 2 minutes. do you hear the clutch fan spinning (it would make a RROOOAAAARRRRRR sound like a MAC truck if it were)? doe this happen every time or just random? is performance affected when you drive or do you just sit and wait for the idle to lower?
its normal for the car to rev high is its cold/been sitting for a while. then it tapers off after 20-30 seconds ish but still revs a little high. once the operating temps gets there, the car should idle below 1k. i think my 2012 is like 800 rpms or somesuch..