What's wrong with my 1993 mazda 626?

My water pump went out, so I had a friend fix it.He said it was pretty difficult because he had to remove the timming belt, and so on... He then replaced the pump and put my car back together. When I start my car it doesn't idle. He checked the timming belt, andhe tried to adjust the idle.I think my friend is stumped,so I drive my car and it constantly dies on me at every stop sign or light. What else could it be,to make my car not idle?