Mustang Stalling Problem

[TITAN STANG]

Hey guys, My Mustang is a 90 LX, 5 Speed, Stock Engine car. It has this damn problem that is getting on my nerves. When the car is under operating temperature, sometimes at operating temperature or when the temperature outside is cold. The car will stall when I let go off the gas pedal. It is not everytime that it happens. It is less frequent when the car is at operating temperature and when the temperature outside is hot enough (70F+). I have already replaced the Idle Air Control Valve and the next morning it did the same thing. Whoever gives the solution to this problem gets a free six pack from me!!!