1995civicex16

We have a 1995 ex with AT you can drive it for awhile then its like it just goes into neutral park is the only settin it recognizes but if you shut the car off and start it right back up it will go right into gear and drive for a ways then does it again.When it wont shift the idle goes up and down constantly like from 800 to 1300 as with the tranny if you shut it off on restart it works fine till the tranny messes up again anyhelp would be great.