Already did Sherlock-Cyberpunk, so Iron Man-Bike:
This was a thing I tried to do for a prompt asking for Cap and Tony getting down on a motorcycle (because ‘Tony is a secret machine fetishist’ but I don’t know about that ‘secret’ part). I actually have three different docs with different attempts. The third is the best-written, but the first one is my favorite, even though the POV switches randomly. Here’s possibly my favorite excerpt (from version 2):
Steve knelt on the cement floor before his custom Harley hardtail, wearing jeans, a thin t-shirt and a fair amount of grease. Attention bent fully to the task before him, his hands moved confidently over the machine as he inspected, cleaned, and tuned it inch by inch.
It was sexy as hell. If this was what Tony looked like when he worked, no wonder people liked to watch him in the shop.
“Has anybody ever told you your bike is a masterpiece?” Tony asked, running his eyes over the curvy bars of the frame. “Whoever chopped that thing was a virtuoso.” Cap had told him the man’s name more than once, but Tony could never remember it. It was just some guy he’d never heard of who was an artist in metal and rubber, who’d updated the machine to 21st century street legality without ruining the lines, then added some ‘special features’ for good measure with minimal sacrifice in looks or performance. Just thinking about it made Tony itch to get his hands on that bike and outdo him.
“Stop looking at it like that.” Steve’s amused voice echoed off the concrete walls. “I can tell what you’re thinking.”
“Yeah?” Tony strode over to leer down at the engine he wanted to disassemble and rebuild. “I wouldn’t hurt it.”
“Stop undressing my bike with your eyes, Tony.” Cap thwacked him on the knee with a rubber mallet without bothering to look up from his work. “It’s too young for you.”
“It’s older than I am.”
“Vintage, please,” Cap said with a pained expression.
“Vintage,” Tony agreed amiably. “Like fine wines and its owner, it ages extraordinarily well.” He laughed when the back of Steve’s neck went red. Then, giving into temptation, he reached out to slide his palms over the contours of the tank and the long leather seat. It felt a little like Steve himself, hard and sleek, part living warmth and part smooth, rounded metal.
He noticed Steve watching him, the man breaking focus for the first time since Tony had come into the garage. More properly, he caught Steve following his hands; so he splayed his fingers and trailed them slowly back over the tank, and came up with a plan. “Would you take me for a ride?” he asked with a grin.
Steve eyed him narrowly, clearly suspecting quite rightly that he was up to something. He gave Tony a once-over, then a slower, calculating twice-over, and asked, “How would you like to drive?”
Tony should maybe have been concerned about the little smirk Steve gave him when he agreed, but it looked too good on him to question it.