89 culass supreme..code 32

just rebuilt this 3.1 from the bottom up. even replaced most of the sensors, hoses. ran good for about an hour and a half with no codes. took it for another run down a long hill with the throtle closed, just coastin down at about 55mph and it popped a code 32. the crazy thing is i replaced the egr, the canister purge valve, and the map sensor already, the 3 things the code book says it could be. don't know where to look now. would appreciate your help.