IAC refers to your idle air control, it meters air at idle and startup, whenever your throttle body is closed basically
TB = Throttle body
UIM = upper intake manifold (plenum) you want to pull the intake tube off your throttle body, take a flashlight, and look down it while holding the throttle open. If you see coolant, that is the problem he is referring to.
heater core is bypassed? How do you heat your car?
Either way, a small amount of coolant can make a LOT of odor believe it or not. You could possibly be looking for a very small leak, or even just some that was spilled in a place that air moves over so you continually smell it.
2002 SLE Dark Polo Green Metallic