Here's the problem:

The brakes on my sister's Integra ('93 RS) operate perfectly about half the time and the other half of the time the pedal sinks completely to the floor. It seems like it's every-other-time I apply the brakes that the pedal goes to the floor, but it's not quite that predictable.

When the pedal sinks, it feels like what happens when your fluid boils (i.e., the car still stops, but the pedal travels much further). But I know that's not it because a) I put ATE Super Blue in there a few days ago and this is just street driving, and b) the pedal works perfectly half the time.

I've changed out the pads and rotors recently, flushed the lines twice and bled the lines four times, but the problem remains. She needs to drive across the country in about a week, so I'm pulling my hair out trying to figure this one out.

Any suggestions?

Thanks!

Adarsh