Did you change the gasket between the TB and the plenum? You may have air coming in there thats not metered and making it idle a little higher.

 

I just installed my new trick flow plenum and it had the 3/8 hose inlet so I didn't have that problem. With the 1/4 inlet you have I guess you'r just not getting enough airflow. I would think that the computer would fix this, though.