For a 103 TC to be built to a 136 requires a lot of work. It is not a upgrade it is a re engineering. Because of the tuning requirements it would not be possible for us to even guess at the cause of an idle issue.
We can bet it runs hot as heck. As cluchglass mention if so called parade is enabled it could cause that on a build like that. I would fine it hard to understand why the tuner enabled it.
It may just need the idle set up a bit. But that requires a tuner to do it.