Okay, something is up and I can't track it down. I suspect its a vacuum leak but there feels like plenty of vacuum when I pull the line.

Sitting at stop, warmed up, if I press the brakes FIRM they go down furher than they should and the engine revs go up to about 1500rpm then settle down. When I let go they drop again. If I pump the brakes I can even get the revs up to 1800 or so. Even without touching the brakes my idle is rough and a little erratic. (It just drifts between ~700-800, not big spikes or anything)

This is DEFINITELY not electrical draw on the system from the brake lights which someone I asked once suggested.

The brakes definitely feel like crap. All the calipers are working (2 brand new) and the fluid is fine. (Just did a full flush and bled it like 5 times) I suspect the master cylinder is shot and I've got a replacement to install but I don't figure that would cause the revving issue.

I've pulled the vacuum lines off the brake booster and there's plenty of vacuum. Don't have a vacuum guage though so I can't tell if its within spec or what. I did all the helms manual checks for the brake booster, check valve and whatnot.

What am I missing?

93 Civic Si hatch, BTW.

 

I am experencing the same problem, I believe it is related to a vacuum leak that I have some where on the manifold.

 

those 2 lines you pulled need to be replaced, trust me

 

The brake booster diaphragm is leaking.

That is why your brakes feel like crap, as you have no power assist, and the pedal goes further down...

Also explains the idle, as you are sucking air from the hole in the booster...