2000 Alero 2.4L will not start cold on 2000 Oldsmobile Alero

When the temps are below 40degrees, it doesn't want to start. we have to keep the rpm's up to 2000 until the temperature gauge reaches half, and then power shift it to start. Then runs rough for another mile or two..then it's fine! have replaced fuel injector, and coolant temp. sensor. have replaced fuel pump system. Out of ideas here! My daughter needs her car to RUN! Help please!!

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