2000 Toyota Echo idles low, rough

My wife has this 2000 toyota echo. Everything was fine until I had her bring it to the garage to have the power steering belt tightened(which became very loose for no reason) and they put a new belt on upside down. Well it rolled up on top of the pully causing alot of stress. My wife drove it home from where this happened(about 4 miles) and now it idles low, runs rough, it drives but looses brake preessure and has no power and is hard to keep running(like if the timing was off). Yes I did replace the belt the correct way myself. When I brought it back to the garag to have them look at it they said it was the map sensor, but they replaced it twice and that did not fix the problem. So after abot a week of them working on it I had it taken back to my home. Is there anything else I can look for since the garage ai go to doen't have a clue.I really need this car repaired and if I can get the answers to do it myself I will, but I don't know what to look for because of the way it happened(power steering belt). Got any suggestions? Thanks