A SMELL COMING FROM AIR VENTS??
Does it smell a little sweet? If its a somewhat odd but sweet smell, your heater core is going bad, and what you are smelling is antifreeze, which is bad...
In some climates, using the Air Conditioning, then immediately turning the car off can cause mildew and a bad smell. To prevent it from happening in the first place, always turn off your A/C about 1 or 2 minutes before you park, and put the fan on high blowing ambient air. If you can't seem to get rid of the smell, I'd suggest running the heat on high for 5 minutes or so. Failing that, you can clean the A/C coils under the dash or turn it on re-circulate and spray Lysol in the ducts.
Search Toyota Celica Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Toyota Celica Experts