92 paseo, need help

i got a 92 paseo that just got a used japanesse engine into i think its a 5e-fe 16valve engine. well the engine got mounted and all worked well, however we took the car for a spin and when we came back it just turned off. and it keeps on vibrating when its on reverse thats when it shuts off. my friend says its the timing but frankly we dont know. any body know why this might happen. its an automatic.......