If the batteries had leaked acid the board is probably corroded. Look at the ground under the steering column (you'll need to remove the under dash cover). As for the erratic idle is most probably due to the Idle Control Valve (ICV). Remove it and clean it with carburator cleaner as it gets full of gunk. If that doesn't help it might be defective and needs to be replaced. Your car might also have the Idle COntrol Module (ICM) which sends the signal to the ICV and they work together.