Thank you very much for the positive feedback. I remember how much time ive spent back then to get all the information and experience and helping you out with it makes me happy :)

The problem is the trading against Pantheon pre 6 which means the first 5-8 mins of the Laning phase. His passive is so strong against Fioras so that you will never have a chance to retaliate before being able to all in with your ult. With ultimate ready, Fiora is of course stronger in the 1vs1 since Pantheons ult doesnt give any duel advantage

Dont give Rumble a chance to kill you. Miss cs if needed, just take xp so that he cant come into snowballing. At level 6 you can all in him and he will not be able to deal as much damage as you will deal. He also does not have a dash so you can easily hit all 4 Vitals of your ult.
Conclusion: Dont die pre 6, all in post 6

As soon as you manage to block his stun and stun him, you are able to go in. Long trades will be won by jax so try to block his E, Q in and give him the E auto attacks. If he is critically low, keep going if not retreat so that he cant W you twice.
At 6 you have to do the same: If you are able to get your ult on him without his E, you can hit all the Vitals.

a tip for hitting all vitals would be to hit the Vital behind your opponent first with using your Q as Jump
Watch my Fiora Montages maybe youll see me using my ult once you can learn from that
Watch some of my Fiora Montages

One think Rengars always to is use their Power of the 5 Ferocity ability. In a duel, they either use their Q or E with 5 Ferocity. Keep your eyes on his Ferocity bar.
Also, you should stay defensive or "tower hugging" like you said until level 6 since your ultimate gives you amazing duel power and his does almost only give Roaming strength.
Dont randomly initiate a Rengar, wait until he uses his 5 ferocity ability for CS, or his W for some heal. Then engage and he will have a hard life to outtrade you.
Summary:
Defensive until level 6
Wait until he uses 5 ferocity ability on minions or block the 5 ferocity ability

Little general tip which could be helpful as well: If you see Rengar walking into a bush, search for your lowest HP minion. He will mostly jump on it for the last hit which you can predict for a great initiation since Rengar will be off-guard

Ps.you guide helped me a lot wihle maining fiora

It's an adc's auto attack in midgame so i have to point out that you get more HP. But yea as you see there is very little real better at black cleaver but the price.

Yes you are right. This Guide lacks of Matchup information i will try to add some more in future (neeta play some Fiora top for that :p)
Since Rumble (for me) counts as Ranged champion with his Flamethrower, Rockets and ult, you have the weaker position generally and especially early. You can only win vs Champions like Rumble (counts for teemo or Quinn as well) with a straight ALL-IN. Your problem as fiora is that there is no well working all-in possibility before level 6. It's important for you to survive the first 6 levels and dont give him a kill as advantage. Don't feel bad about not getting some last hit Gold as long as you can survive in lane. At level 6, wait for him to come near you for a little Rocket or his Flamethrower and then dive into him and cast your ult. He will run away, you will kill him or at least get him out of the lane and get a huge advantage.
A little strategy would be:
100% Safety as soon as you enter the Toplane -> Don't care about getting cs, best case you get some but what really matters for you until 6 is your EXP, not the Gold. -> When you hit lvl 6 you probably got poked a bit so leave lane, buy a Long sword or in best case even the Tiamat and then return with your teleport. If he stays, all in with ult, if he left, push lane. As soon as he pushed the lane back which most Rumbles do with his great Waveclear, wait for him to go for a poke and all in.
A little tip for the ult all-in in general is to wait for a vital to appear next to you so that you can Q to him and hit it and then cast your ult because you will hit a total of 5 instead of only 4 vitals then.
Good luck against your future Rumbles :)

First of all, you have to remember in what way your opposing Yasuo initiates his trades. Most of them E in auto attack and Q you and try to get out as soon as possible. What you can do is:
Before 6: W as soon as he comes close because you will not take his Q damage, deal damage to him and on the top which almost noone knows, you will shred his attack speed with your W so that you can start a trade with your Q and E afterwards.

After 6: If he runs into you, instantly all in him so that he has no time to prepare his knockup. It's always important to destroy your opponents plan and play your own plan.

Your biggest issue was his Whirlwind so let me talk about this a bit.
Most Yasuo players (from my experience) try to get the EQ combination on me with the knockup so that its a safe one. You can predict his Q then with instantly going into W when he dashes into you with his knockup. After some times youve outplayed him, he will keep this in mind and E into you, wait one second and knocks you up after he dashed through you so that you cannot block it anymore. A simple counterplay to that is that after using your W you instantly Q orthogonal to yasuos Dash (90° degree) so that even if he waits for your W with the knockup, you would anyways dodge the Whirlwind with your Lunge afterwards.
I wrote some lousy english here, hope you were able to understand something :)