I just bought a '90 Integra with a B16a2 swap. I drove it about 300 miles and the brakes started acting up. Whenever I'm at idle or coming to a stop the brake pedal gets really soft, it almost goes to the floor, and the brakes don't work well. I do have some brakes - enough to hold the car in place or slow it down with help from a downshift, but they're bad enough that I don't want to drive the car.
Also, the engine RPM's fluctuate at idle when I step on the brake. The harder I push on the brake the lower the RPM's go, but the car never actually stalls.
Someone told me that the PCV valve may be bad, but I thought it might be the vacuum booster. Any input would be greatly appreciated!

 

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