Stalling at red lights?

I had a power steering leak and an oil leak on my car, got a new power steering pump and fixed the power steering leak. Then I had an oil leak fixed by a mechanic replacing timing, water pump, all seals hoses, and gaskets, including head gaskets. The only seal not replaced was the rear seal, but the oil leak was fixed. When I took it to the mechanic it ran fine other than leaks; now that I have gotten it back it stalls when I stop at a red light, but when it's in gear and idling it runs just fine and it runs fine when I'm moving it just stalls at a red light.