P1457 HONDA -

Question

My car is a Honda Accord LX 1998, 4 cyl. I have P0172, P0420, P1457,  and P0170. My question is what would be the underlining issues? Car runs great. Only thing I have noticed is that when I get it about 2 miles down the road it is almost as if the car shifts down then shifts back up, and when I stop the car and put it in park, it will tend to almost shut off. (Im thinking that the RPMs are so slow it almost shuts off, never has though.) I am looking to sell my car so I want to fix the problem before selling it.