I bet it's not a FITV...

Buddy had same problem, too much of a vacuum leak, he had a VX shell from the junkyard, after having the idle problem for like 4 months, and having checked EVERY vacuum line, we couldn't figure it out...

Everyone always just says "vacuum leak" but that doesn't really help, we replaced every vacuum line and found out it was a vacuum leak, but it was NOT on a vacuum hose, it was the actual seal around the brake booster, mounted on the firewall in front of the driver.

I bet this is your problem, although having swapped it into a mini, i don't know how the brake booster is set up.

Nice swap though, nice to see something that is new...
Good luck!