2007 Lincoln MKZ Question: Car will not start in cold weather

great cranking power, will not start when the lows dips to 20s, when the out side temp warms to mid 30s starts great. It was in the Lincoln dealer two weeks, no codes will show, they replaced throttle plate, replaced spark plugs still will not start,
I have had this car to 2dealers, They say with no codes showing all they can do is start replaceing parts, is this true? no one has talked price.