The charcoal filter was an option. On a 94, i believe if you have it, the hood itself has the lateral slotted louvers toward the rear of the hood. If you have a flat hood, no louvers, you don't have charcoal system. you can also tell by the charcoal switch on the dash to activate the system. IF you have charcoal system, the charcoal filter is replaced only every 75,000 miles, but it costs in the neighborhood of $400 to $500
and about 2 to 3 hours to replace
! The wiper assembly has to be removed to access it.
Then there is the filter Benzmac mentions, this is called either the "dust filter" (if the car has NO charcoal system) or the charcoal pre-filter (if it has charcoal system). If it is a no-charcoal system car, the "dust filter" is pretty cheap and is replace every 15,000 miles. If on the other hand it IS a charcoal system car, the charcoal pre-filter is a little pricey ($100-$200?) and is done every 45,000 miles.
The third filter is the recirc (recirculation) filter. This is the same on both versions, it's just a sheet of a white fiber mat material, very cheap. It's the only one located inside the cabin, under the dash in the passengers side footwell area. it's done every 15,000 on both versions.
PS later on in production of the 140, ALL had the slotted hood, in that case the only easy way to tell if it was a charcoal system car was by the switch for the charcoal system.
Also to clarify, ONLY the charcoal system cars have 3 filters:charcoal pre-filter, charcoal filter and recirc filter.
NON-charcoal cars have only 2:the dust filter and recirc filter.