Rep Power: 0

I have been having cold start issues where my car won’t like to start after sitting for over a hour, sometimes I have no issues and it starts rait up sometime I won’t start at all, but after it starts it will smoke pretty bad and not want to idle until I redline it then the smoke clears up and it runs perfect, bought it a couple weeks ago and old owner said he did new engine 3,400 miles ago I plugged scanner in and is says PO 505 PO300 (from startup) and PO420
any advice would be greatly appreciated