Okay, even though everyone here is technically giving you the right answer, the reason you're not seeing improvement is you're not practicing the right way. You've hit the wall of what you can do without good lookahead and smooth turning.
So, GO SLOW AND LOOK AHEAD. What that means is, stop trying to solve quickly. Turn slowly enough that you can stop looking at your current F2L pair, and start looking for and planning the next while you execute.
If you're having trouble with this, try solving F2L pairs with your eyes closed. Scan the cube to find the pieces, close your eyes, then pair up and insert. Once you can do this easily, open your eyes and while you're moving your hands, scan the cube for the next pair and figure out what moves will insert THAT pair. Once you can do this really well, you'll start to see those sub-30 times.