i put a 91 5.0 in my boat and i am having problems with idle. it doesnt idle and it runs real rough. i pulled codes and heres what came up. 31,67,81,82,84,85. i am not running smog equipment so i know that 31,84,85 are issues. 67 is nuetral safety. does this affect the way the engine runs? is my IAC bad? i bought it brand new, can i test it?