Well i just put in a 89si motor in my 91 civic dx and just used all the part from my 91 it runs fine but when i step on the gas i get no responce. what i mean is when im drive and i go to spet on the gas i get nothing but when im on the highway it is fine at high rev but if i slow down say like in 5th and then try to step on it again i got nothg so i have to shiff down it 4th to get the revs up again and then back to 5th.

 

check your o2 sensor levels, see what it's reading, also your ingnition wires, could be an arc going on

 

how do you check the o2 sensor