Have you checked your oil pressure switch?  Try to bypass it and see if it will idle down. Also if it is low on oil, sometime that will cause it to idle up.

The PC board only idles your machine down, it times out and grounds out the 12volts idling you machine down. If you machine won't idle down, put a jumper wire across the screws of your oil pressure switch, if it idles down your switch is faulty. The switch is satisfied by 8 psi. Is your green light on? Keep your old board because that wasn't the problem. Also when you installed the new board did you clean the spacers. The spacers are where the board grounds out.