'99 Blazer--Braking affects engine idle?

Ok, here's one for you experts out there.
I have a '99 4-door Blazer (4.3L) with just under 30K that seems to have a squashy brake pedal. I say "seems" because 1) I have nothing
to compare it to, and 2) The brakes still stop the vehicle reliably. I would just expect a firmer pedal from a vehicle this size.
Today while parking, I noticed something I thought was kind of wierd. While sittng in any gear, stepping on the brake pedal hard causes the engine idle to increase about 100 RPMs. If I do it 3 or 4 times, I can raise the idle speed from around 500 to 900 RPM. Is this a normal function of a vacuum-assisted brake booster, or do I have some kind of leak here?
Thanks for any assistance,
Not Dead Yet
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That is normal because you are introducing air into the intake track through the booster. Don't just sit there and mash the brake down for hours in a parking lot. You probably have a weak brake hose or misadjusted rear shoe. It has three brake hoses. One for each side in the front and one at the center in the rear.

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Thanks for the reply,
Introduction of extra air into the engine through the booster is normal? I guess I do not understand the construction of the brake booster very well. Is there typically some kind of seal or gasket that could be failing, or am I looking at some kind of structural failure (no rust or cracks tht I can see)? This part does look like it would be a real bitch to get at and replace. Of course there may be other things happening also.....
I have checked over the mechanicals (front and rear calipers and hoses) and have not found anything obvious. The fluid levels in the master cylinder resevoir has not changed, just the pedal "feel". I do realize that no one can troubleshoot over the internet with 100% accuracy. I'm just looking for some pointers on what to keep an eye on.
Not Dead Yet
On Wed, 8 Jun 2005 07:18:00 -0500, "noname"

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The idea is really simple. Its hydraulics. You make pressure one place and the fluid transmits that into motion and back to pressure at another place. If you have a weak point in the system, you will be wasting the pressure thus changing the way the pedal feels to your foot. Have someone else press on the brake pedal and watch the lines and hoses. I they move alot under pressure, they may be some of the loss. The auto adjusters on the rear brakes can be seized up and not rotating to adjust the shoes. This would require more pedal travel as to take up the loose setting of the shoe to the drum. A 99 model with those few miles probably sits alot and rubber brake parts are the first thing I'd check. The master cylinder and booster should be replaced as a unit if needed. The master cylinder can bled off pressure also. The booster may be bad. You mentioned the high idling, which most of the time some is normal. But too much vacuum loss would mean not as much force to boost, thus changing pedal feel, and introducing air into the motor. An experienced brake guy could figure it out in less than 30 minutes and recommend a solution.

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