Erratic brake performance due to rough idle?
 

Totally throwing a theory out here.

I have noticed lately that occasionally when I push the brake pedal it will seem to "slip" a little? Very hard to describe. It will start to feel normal, then the pedal will almost feel like it is dropping suddenly to where it is not a smooth push. That's the best I can descibe it.

This is always at very low speed, like navigating a parking lot, and it's never resulted in poor brake performance overall, the car still stops where I want it to stop. But again, we are talking about < 10 mph here. It's never done it at any higher speeds, which is good for safety, and also lends towards my theory.....

Another thing is VERY occasionally, like maybe 1/4 of the time it does the above symptom, it also makes an audible "electronic" type of buzz for a second. Again, hard to describe, but almost like a little pulsing buzzing sound? About 1 second total, and always with that erratic brake behavior (although again, the sound only happens about 1/4 of the time).

I've had the car into a trusted shop to check on some things, this included. They went over the whole braking system and couldn't find anything visually out of place. It's not like they tested the sensors or electronics, but all the physical components looked and acted as they should (and of course on the test drive nothing acted up as usual!). All rotors and pads are brand new, as well as fluid flushed with new. Stainless lines and calipers are at about 20K miles.

So now my theory/question. Could the electronic braking system in the SVX be affected by the rough idle issue I have? At stop lights and low speeds I do have issues with rough/fluctuating engine performance, which I'm working on (probably will do new TPS next). Could this possibly affect the braking system, like is it RPM sensitive, or maybe cause a power drop that affects the electronics? Or am I dreaming and should have a more thorough inspection done on the braking system electronics?

Re: Erratic brake performance due to rough idle?
 

Makes sense..... the vacuum may not be sufficient when the idle is stumbling, and when the SVX is going very slow, its always right around idle RPMs. The vacuum in your booster might not be enough to keep adequate boost so that may be what youre feeling. Also the check valve which keeps vacuum applied to the booster even when the car stalls or has momentary low vacuum could be going bad allowing vacuum to leak back into the supply line from the booster.

Re: Erratic brake performance due to rough idle?
 

Thanks!

Like I said, my next step is to replace the TPS. I'll report back if this has any effect on this issue as well.

Re: Erratic brake performance due to rough idle?
 

Have you tested it first? Pulling the TPS is pretty easy so its worth the time to test the resistance arc first. Rough idle can be a PITA to diag..... does it do it all the time...or just when cold or warm?

Re: Erratic brake performance due to rough idle?
 

Could be the ABS. My pedal will pulsate slightly if I happen to hit the brakes at the same time that the ABS runs it's self-test. (You can see it at night, when you start that car and hit about 2-3mph while moving forward, the headlights will briefly dim slightly, that is the ABS pump doing a self check.)

Re: Erratic brake performance due to rough idle?
 

So THAT's what that is. I had been wondering, I've felt it a couple times when I first touch the brakes in the morning.

Re: Erratic brake performance due to rough idle?
 

Any time I think of buzzing or pulsing in the brake system, my number one suspect is the ABS pump or relay. I too have noticed the ABS self-test thing like Crazy_pilot and Hondasucks have noticed.

Re: Erratic brake performance due to rough idle?
 

That was the first thing that came to my mind - the ABX pump. I don't know how it is associated with your problem, but maybe something. :o

Re: Erratic brake performance due to rough idle?
 

Troy, trying pulling the two plugs for the ABS pump. This will disable the pump from working and default the brake system to a Non-ABS type. If this fixes your issue we may be on the road to finding the true cause of the issues

Tom

Re: Erratic brake performance due to rough idle?
 

Thanks Tom. Once I get the idle issues fixed if the brake issue persists I'll try this. Like I said, the brake thing doesn't happen that often. I could disconnect the pump and still not know if it changed anything for weeks.

Re: Erratic brake performance due to rough idle?
 

There was a problem with some of these systems that would cause the ABS pump relay to stick "ON" causing the pump to run continuously, even with the key off, which would drain the battery. It could be a defective relay causing the pump to cycle long enough to feel it in the pedal, which would explain the noise... I'm not talking that it's making it run all the time, but like if the contacts were bouncing around causing it to like, pulse?