It's possible that the new fan is pulling more power. You know how when you turn on the A/C the engine revs up a little? The fan might be pulling more power than before for some reason. I'd try pulling out fuse #11 (computer) and putting it back in to reset the CPU. That MIGHT fix it. If not, the Haynes manual says that you cannot adjust the idle and to take it the shop. Hope it works that way but if not you can always go back to the same shop and they should be able to adjust it for you. Just tell them they didn't fix it right.
