brake pedal slowly falls to floor at stops, i have checked the vac pressure on the manifold, leaks on the master cylinder, the check valve for pressure calipers are not leaking (no open spots in the system). this only happens when it is warm outside or the a/c is on.... i am frustrated because i should know whats going on but i have not found any resolve to the situation. any thoughts?

 

sounds like the M.C

pump the brake pedal 5 times fully with the car off and then hold it down and start the car,if it goes to the floor then it most likey the M.C

 

how old is the fluid? any recent brake work?

i agree on the booster test for sure, but keep in mind, brake fluid is extremely hygroscopic. meaning it absorbs moisture. if the fluid is old enough, there's a chance that it's absorbed enough moisture to give a spongy pedal. just a thought. most people almost never replace the fluid and it's only got about a 3 year life once exposed

although it is more than likely a seal in the master cylinder.
if the booster test passes, i'd probably just replace the MC. assuming that no recent brake work had been performed. i like to bleed at the lines off the MC once installed, as well as bench bleed.
that takes away the need to bleed at all 4 corners. and sometimes you'll get air trapped up in there that can't be expelled through the bleeders
but you should still bleed at all 4 corners to remove all the old fluid

 

I'm going with MC, [blowby], check up on the inside of car, is #4 the rod seal... http://www.acuraautomotiveparts.org/...ystemcomp=List All&vinnoT=&trim=&trans=&view=normal
"wet" with BF, if so the piston seal is gone and brake fluid is "blowing by it", "it blows" back when you take your foot off the brake, [a leak, just not an external one].

I speak from personal experience, identical symptoms, [except for the A/C] happened to my 94 Integra. 94

 

wonderful, all of this makes sense along with the theory of blow by, being that no recent brake work has been performed, and that there is not a loss of fluid in the sytem.. the blow by or contained leak seems to be the reason for this. its not loosing fluid but rather pressure in relation to the pedal to the internal seal, thanks