If you aren't 100% sold on the idea, try temporarily plugging it up. Hand cut a small piece of cardboard into the shape of the mounting gasket but don't add the vacuum port hole through the middle of it and test it out. If it solves your running problem you can then choose to either permanently seal it up (epoxy, JB weld etc) and delete the HAC completely, or seal it up and re-mount the HAC solenoid to keep it looking like it's functional.