You may have to check every inch of vacuum tubing for cracking. I have an older Chrysler minivan and quite a bit of the vacuum tubing is hard plastic and only small sections are rubber tubing. While trying to track down the cause of rough idling, I discovered a crack in one of the hard plastic lines. It was in an area where I have to reach into during routine maintenance. I cut out the cracked section and replaced it with a piece of appropriately sized rubber tubing. No more rough idle. Don't forget to check any fittings in those vacuum lines too.
2016 Minnie Winnie 27Q on a 2015 Ford E450 chassis. Retired U.S. Air Force. Living in Anchorage, Alaska