You could try a couple of types of spray around the intakes. Use a spray can with the long plastic tube inserted into the nozzle. you can pinpoint where the vacuum leak" is. Vacuum can't "leak " out but air can leak into it because the seal is not sealing. A ether base spray would speed the engine up and a spray like WD 40 may smooth it out for a few seconds before it gets pulled in by the vacuum.
