1990 Geo Metro Starting problems

My Geo Metro will not start and run if the temp. is below 30 degrees. It will start and run for about 20 seconds, then die like it ran out of fuel. I can have the throttle open most if not all the way and it still dies. I have replaced the coolant temp. sensor and the throttle position sensor. I have tested the air temp. sensor and it tested good. If the outside temp. is above 30, it starts and runs, but not too good until it warms up good.