Several Engines are possible. My personal opinion is the 7MGTE is the best engine for the car, however the 2JZ-GTE found on 1993 and up will give you more power. Also, the 1JZ-GTE can be swapped in....
Its usually an emissions thing (bad O2 sensor). But don't guess, just get the code read, you can get it read for free from almost any major auto parts store, then google the code for an answer.