idle erratically
 

i have an 89 crx the prev owner put a d16y7 engine w/ auto transmissionin it. lately it has been acting up when i have it in park or neutral it willidle erratically but when i put it in gear it stops then when i am driving and i slow down to stop it almost sounds like it's going to die then it will rev back up. any ideas of whats up with it. thanks