Still don't know how to "explore the vents". Went through the vents with the spider webs and got the pheromones but now I'm stuck.
Well, I hate to be the one to break it to you, but you have just 'Explored the Vents'. 'Explore the vents' is literally, your character moving around in the vents. There is no 'explore the vents' button, it is just you moving your character around to various places in the vents.
Have you found AMI? Have you found Nyun? Have you found 'the next sector' of the vents? Did you discover the 'stealth module' upgrade for Tali's suit? Have you discovered the two 'upgrade' programs for AMI?
Have you gone to the second part of the vents and been prompted about entering the bridge? (<- Leads to end of game)
If you have, you have explored pretty much everything to find in the vents.