OK, that's probably why you've got leaks now. The butterfly plate needs to be centered up in the bore before you tighten the mounting screws fully. With the mounting screws just snug and the return springs installed on the butterfly shafts, open the butterfly fully by hand and let it snap shut. Do this several times then finish tightening the mounting screws.
When you install the plates and tighten the screws before installing the return springs, this can cause the plate to bind in the bore. The spring pulls the shaft towards it slightly. That's why you need to go through the "open fully and snap shut" routine after you install the springs but while the plate mounting screws are still loose. That centers the plate for you and relieves the binding.
What's happening in your case is the butterfly plates are probably not closing fully. Most of the way, yes, but probably not 100% like they should. Since they're binding, that is pushing the shaft hard over to one side in it's pivot hole which is probably responsible for the leak. The leak combined with the plate not closing all the way is giving you the racing idle.