1984 California cars do NOT have a trap oxidizer, 1985 cars DO.

1985 cars also have a significantly more "Rube Goldberg-ized" emission control system with many more vacuum valves, vacuum lines, solenoids, etc. More stuff to go wrong, IMO. Conversely, when I was looking for my 123, I drove two 1985 models, and they both drove very nicely - the trans (modifications?) are very nice, and they both accelerated just as well as the 84's even though the 85's have a slightly taller rear end ratio.

There were several addtional changes for the 1985 model year nationwide, which means some parts are not interchangable with the earlier years, therefore your supply pool is somewhat limited when looking for certain used parts.

RTH