Tony is in his workshop and Steve comes down. The part that I remember is Tony watching as Steve punches his pass code in and musing about how quickly he always does it like he's afraid he has to do it quickly or it won't work or something. And how no matter how fast he punches it in, he always gets the code right.
Yeah, almost nothing to go on, sorry.
I can tell you that it was definitely Steve/Tony (could have been pre-slash) and that it was definitely on Ao3. I think it was probably over 10K. I know those things simply because my only Avengers reading has been on Ao3 and in the steve/tony tag and that I always use the word count filter and I haven't made it down into the smaller word counts yet.
This is kind of a last ditch effort on my part to find this fic because that particular scene keeps scratching at the back of my mind and I'd really like to fill in the blanks again. Thanks!
(I honestly can't be any more specific on the tags since I remember so little from the fic itself. :x sorry)