From what I remember Tony has autism/aspergers or something like that. He had some sort of problem. I believe that he was afraid to tell the team but they find out. I remember he has problems with being physically weak and cannot do strenuous things for an extended period of time. Clint and Steve help train him using trampolines and stuff in the gym and help him build up physical strength. I think at one point JARVIS gets hacked and Tony has to climb into the vents to use the arc reactor to get rid of the hackers and can manage to hang from the vents due to Clint and Steve's training.
If anyone has knows what this is please send me the link and if you have any other fics like this feel free to recommend them!