Rough Idle

I have recently had my car tuned with a mustang dyno, When I got the car back the HP was a lot lower then it was rated for as described in another thred I posted. But the problem I am facing now is when I start the car it reves up to about 2000rpm and takes about 10-15 seconds to get down to 900 were it idels at. Then when I am crusing down the road and I put the clutch in it does the same thing but takes only about 5-7 seconds to get back down to idel. But the most annoying thing is sometimes when I put the clutch in the cars rpms drop down to 0 and stalls out and I can understand why! its not all the time but often enough to be a pain in the ass! So if someone could please point me in the right direction that would be great!
Thanks

I thought maybe vac leak to but the idle gets back down to 900 were he set it, but its just a little slow. I should take it back and have him fix it, but I don't want him to mess anything else up, not sure if he really knew what he was doing. also still not sure about the stalling?