In most cases, the ports are plugged just below the removable plug where it enters the intake manifold. I used a small drill bit mounted on a 1/4 in rod and just hand twisted the bit in to open the port. I wouldn't use oven cleaner. In extreme cases you might need to remove the other two plugs and clean those ports. The new plugs are like small cups that are pushed into the hole with the botttom side up.