2003 chevy impala gets hot when idle only cools when in motion need to know why

If it overheats in traffic, it's most likely caused by failed cooling fan operation. If you're moving, air flow moves through the radiator and cools the coolant. If you're not moving (Idle in traffic) then nothing cools the coolant -- except the fans. Check there first. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops