Hello everyone. This is probably a previously discussed topic here, but can anybody tell me what could possibly be the cause of a very bad toxic smell coming out of the left driver's a/c vent ?. Sometimes when I am driving and come to a stop, that awful smell appears. I think it is burnt coolant smell, but everything around the engine and coolant reservoir looks fine. I even took it to a local Chevrolet dealer for service and they replaced the water pump, and the smell comes in from time to time. Any feedback will be greatly appreciated.