engine starts, idles and runs rough when it is cold out until it warms up

This happens when it is cold out (below 20f). The car always starts, but it shakes when cranking and runs so rough for the first 20 min. I have to put it into N at stop lights. There are no engine codes. I have replaced the plugs and wires, engine coolant temp sensor, ambient air temp sensor (located in the air box). All maintenance done, regular synth. oil changes w\toyota filter, clean K&N air filter, replaced transmission and differential fluid (didn't know before this front wheel drive had dif. fluid to change),all belts, hoses and fluids replaced this summer when radiator was replaced (engine didn't overheat, just cracked on top tank). This is the third year this problem has been happening when it's cold and no one can figure out what it is. I would greatly appreciate any help. Thank You