Chevrolet Repair: 2004 impala ss rough/low idle, coolant temp, 2004 impala ss

Question
I have a 2004 impala ss that when first started idles at about 500-800 rpm and a little rough and often dies out or wont start without stepping on the gas. i have replaced the aic on it as the code threw out used to be a high idle, now its the opposite. there is no code being thrown so i dont have that to go off of. just that it usually wont start without stepping on the gas and then idles low and rough for a few minutes then is fine. if you dont let it idle then the car dies out. this is happening more now that it is cold out. any help would be appreciated. oh yeah i did the regular tune up plugs wires air filter oil change

Answer
HI MIKE,,THIS IS JUST A GUESS WITH SO LITTLE TO GO ON, BUT TO ME THIS SOUNDS LIKE A COOLANT TEMP SENSOR IS BAD..IT MAY THINK THE ENGINE IS WARM AND NOT RAISING THE IDLE ENOUGH AND ALLOWING MORE FUEL TO ENTER THE ENGINE BECAUSE IT THINKS THE ENG IS WARM !!!THE ONLY WAY YOU WILL KNOW FOR SURE IS LET THE ENG COOL DOWN, PLUG YOUR SCAN TOOL IN AND CK THE DATA [NOT CODES]
BEFORE YOU START THIS THE COOLANT TEMP SENSOR SHOULD BE ABOUT THE SAME TEMP AS THE OUTSIDE AIR  OR MAYBE JUST A LITTLE WARMER..IF NOT THE SENSOR IS MORE THEN LIKELY BAD..I WILL ASSUME THAT AFTER THE ENG WARMS UP IT IS OK ??? YOU ALSO SAY THAT YOU REPLACED THE  AIC ?? YOU MEAN THE IAC [IDLE AIR CONTROLLER] ??? IF THE COOLANT TEMP SENSOR DOES NOT DO THE TRICK,CK THE BACK SIDE OF THE THROTTLE PLATE FOR ANY CARBON BUILD,IF SO,,, CLEAN IT WITH A CLEANER AND SOFT BRUSH..YOU WANT THIS CLEAN.DO NOT SCRATCH THIS PALTE..LET ME KNOW HOW YOU MAKE OUT..GOOD LUCK TO YOU,,,TOM..