I have an evo 6 has a little idle problem, car has just been tuned. Is stock engine/ turbo.

the problem is on cold start it will start and idle at a normal cold start 1500rpm then after about 10 seconds it will slowly climb up to 2000rpm and then start to drop back down to 1500 as it warms up and stays there. Ill go to drive it and come to a stop and sometimes the idle will be 900rpm and sometimes it will be 1200-1500rpm, just wondering if anyone has had a similar problem?

iv had the throttle body fully rebuilt about 1000k's ago so all the seals have been done and all the carbon has been cleaned out. It cant be the tune cause it was doing it before the tune