While driving normally, when I press on the brake pedal, it'll "attempt" to stop my car but is slow to do so. Doesn't matter how hard I press, it just doesn't stop fast enough and I know I won't be able to stop in time during an "emergency"

I replaced the M/C without change. I've bleed the brakes 2 times with an Autozone vacuum tool and will attempt the "pump the brakes - hold - open the screw" method tomorrow to see if that helps.

I've gone through the Booster tests outlined in the manual and all checks out fine. The only "weird" thing happening is that if I'm idleing and at a standstill, if I press on the brakes, my revs increase until I let off. Is this a booster issue?

 

If your rev's are going up when your dead stopped and you pump your brakes then your M/C is working correctly by drawing the correct amount of vacuume it needs to operate correctly.

Try having a buddy sit in the car and pump the brakes about 5 times then hold the pedal to the floor as you open the bleeder then close it after the pressure is relieved from that side. do it like 2-4 times on each end and get back to us.

 

Bled the brakes again using the "pump - hold - bleed" method and got the same results :-(

Since my car never increased revs when idling and pushing on the brakes, I know something is not right with the booster which affects vacuum and hence revs...

While pressing the brakes at idle, I heard a slight "hissing" coming from under the dash so I layed down underneath and pressed on the brakes - hissing is coming from the hole where the booster rod comes out and connects to the brake pedal. I put my finger in the area on the booster and pressed the brakes again and I can feel the air escaping from the booster. This explains why my revs are increasing - I'm losing vacuum via this hole and the ECU is trying to compensate.

I guess it's time for a new booster but I have 2 used spares in storage from previous cars. I really don't want to spend $100 at Autozone for a remanufactured booster so I'm wondering if there is a way to test these things without having to install them first?

 

It really sounds like you need a new booster if you are losing pressure from where the pushrod connects from the brake pedal into the booster (there is a seal that sits between the booster and the firewall which may be your problem). get one at AAP, I work there and know that they'll cost 69.95 (for an si) with a 25 dollar core charge. good luck

Read this if you need help with removal:

http://crx.honda-perf.org/faq/data/7.html

 

Well, I tried comparing the "function" of the booster out of the car with 2 others I have and they all "react" the same. I tried with the M/C on and off on all three and used adapter plugs on the hard line holes to simulate an in car installation - nothing.

I tried using a vacuum tool I have but I can't build any vacuum for some reason. I even tried blowing through the hole on the front of the booster that goes to the intake manifold via the valve and I can feel the air coming out of the hole where the brake pedal attaches to the pushrod. I guess these tests are not "real world".

Now, you mentioned a rubber gasket that goes between the booster and the firewall - I'll check that out - but does this prevent vacuum from seeping out via the pushrod hole? I also noticed the large rubber o-ring that seals the master cylinder against the hole in the front of the booster - maybe vacuum is seeping out here? Tha manual says to used silicone grease on the o-ring and the M/C rod but I did not do that before installation. As a matter of fact, I actually removed it from the hole on the booster because there was rust and I wanted to clean it.

Maybe this seal is bad and is the reason why vacuum is seeping?

 

Confused on why you think it's the booster.
Is the pedal really difficult to press down on or something?

From how I read this, it seemed like you could press down just fine... nothing wrong with the booster. Unplug the booster vacuum line and then try pressing on the pedal.
THAT's what a bad booster does.

Is you brake pedal squishy are firm?
What is your brake setup at the wheels? - last time you serviced any of them?
-Last time you bled the fluid?

 

With the car on jackstands (after bleeding) and powered off, the brakes feel and work fine on all 4 corners. I turn the car on and let it idle. I push on the brakes and the revs climb. I can hear and feel air escaping via the hole where the pushrod exists the booster under the dash. Could it be the small round rubber seal in between the m/c and the booster in the engine bay? I did not change it or grease it like the manual suggests but it looked and felt fine.

Now if I drive the car, the brakes feel "hard" without much stopping power no matter how hard I press.

 

make sure you bench bled the master cylinder before putting it on and make sure the wheel cylinders in the rear brakes are not leaking that should be your problem

 

When mine did the same thing, I replaced the rear brake shoes, which were badly worn and it solved the problem.

 

Your booster also had a hissing sound under the dash where air (vacuum) was escaping and replacing the rear shoes solved your problem?

 

I did bench bleed the new m/c before installing it. I am not losing brake fluid from any of the four corners.

 

Have you tried replacing the old brake booster with a new one and then taken the time to calibrate it properly in regards to the pedal arm and pushrod adjusting screw? If, like you initially said, the pedal feels fine at first and then gets soft, or goes to the floor, then the issue is definitely a vacuum leak in your booster (which you already noted) or you are losing fluid somewhere along the brake lines (which you said you are not). Also, make sure the rubber seal b/w the booster and firewall is in good shape.

 

did you get the stock replace M/C? Upgrade to the prelude si? just wondering if the parts guy gave you the right part. Your brakes were workin before you swapped it out tho right?