How do I keep my car from stalling?

My car stalled at a red light and would not start back up. I tried reving the engine but as soon as I let go of the gas it would shut off. So I took off the radiator cap while it was still hot,I was expecting it to gush out but it was cold water. We towed it home and I replaced the bad fuses that I think caused this and I took off the lower radiator hose from the water pump and antifreeze came out. I took off the thermostat and flushed out the radiator and the engine through where the thermostat goes. Only a little stream of water came out of the water pump when I did that still woulnt stay running unless I keep on the gas. The garage says its the idle sensor or the throttle pisition sensor.I dont know why the sensors went out because of an coolant issue, and do I need a new water pump too.