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#1
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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?
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Troy 1992 SVX LSL "Serenity" 250,000 miles! I don't care, I'm still free, You can't take the sky from me... Last edited by WestCoastSVX; 03-05-2009 at 11:44 AM. |
#2
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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.
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#3
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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.
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Troy 1992 SVX LSL "Serenity" 250,000 miles! I don't care, I'm still free, You can't take the sky from me... |
#4
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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?
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#5
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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.)
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1992 SVX LS-L #1222 Pearl White 1987 GL Turbo wagon, 5 lug conversion, D/R 5 speed (Rice killer) 1992 Dodge Ram 4x4 diesel (car hauler) 1968 Dodge Polara convertible (Camaro killer) 1990 Toyota Corolla FWD auto (330,000 mile grocery getter) 1986 VW Jetta |
#6
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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.
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Chris 92 Ebony Mica LS-L "A Rolling Restoration": 223,250 KM - Sleeping 2007 STi 6MT, Stance GR+ coilovers, PWR Rad, JDM hood badge, svxfiles 6000K HIDs, JDM Clear Corners, $15/15 min mod, $20/20 min mod, Energy Swaybar Bushings, Hella Supertones horns, Gold STi BBS rims, Group A lightweight crank pulley, A/C system removed, Custom header-back exhaust, Hybrid carbon/metal rear sway bar, restored headlights with CCFL halos 2008 Subaru Legacy Spec B - Diamond Grey Metallic - Sold 2020 Ram 1500 Longhorn - Red Pearl |
#7
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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.
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-Jason (8/23/07-Present) 1995 Subaru SVX LSi (197k) Polo Green (#1102) 03/95 Mods: DDM Tuning 4500k 35w Low Beam HID, 100w H3 Bulbs, Extra Ground Cables, 15 minute $12.96 mod, svxfiles designed transmission mount (), sporting a "new" tail light bar, silver BBS rims, custom power steering cooler (one that doesn't dump ATF constantly), new negative lead cable, no more third or fourth gear (1977-Present) 1977 Chevrolet Corvette (81k) Silver (12/01/2011-Present) 2005 Subaru Outback 2.5i Limited 5MT (97k) I have a bad feeling about this. -Obi Wan Kenobi |
#8
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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.
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. Earl .... ... .... ><SVX(*> Subaru Ambassador [COLOR=”silver”]1992 Tri Color L[/COLOR] ~45K (06/91) #2430 1992 Dark Teal LS-L ~184K (05/91) #0739 1992 Claret LS-L ~196K (05/91) #0831 1992 Pearl LS-L ~103K (06/91) #1680 1992 Pearl LS-L ~151K (06/91) #2229 1992 Dark Teal LS ~150K (07/91) #3098 (parts car) 1992 White LS-L ~139K (08/92) #6913 1993 25th AE ~98K (02/93) #164 1993 25th AE ~58K (02/93) #176 1993 25th AE ~107K (02/93) #215 1993 25th AE ~162K (02/93) #223 1994 Laguna Blue Pearl LSi ~124K (1/94) #2408 1994 Laguna Blue Pearl LSi ~144K (10/93) #1484 1994 Laguna Blue Pearl LSi ~68K (10/93) #1525 1994 Barcelona Red LSi ~46K (02/94) #2624 1994 Pearl LSi ~41K (12/93) #1961 1995 Bordeaux Pearl LSi ~70K (02/95) #855 1996 Polo Green LSi ~95K (03/96) #872 1997 Bordeaux Pearl LSi ~55K (08/96) #097 2003 Brilliant Red LS1 Convertible ~29K (04/03) #8951 1999 Magnetic Red LS1 Coupe ~33K (04/99) #6420 My Email | Old Locker | New Locker | Picture of 15 of the 19 |
#9
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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 |
#10
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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.
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Troy 1992 SVX LSL "Serenity" 250,000 miles! I don't care, I'm still free, You can't take the sky from me... |
#11
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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?
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1992 SVX LS-L #1222 Pearl White 1987 GL Turbo wagon, 5 lug conversion, D/R 5 speed (Rice killer) 1992 Dodge Ram 4x4 diesel (car hauler) 1968 Dodge Polara convertible (Camaro killer) 1990 Toyota Corolla FWD auto (330,000 mile grocery getter) 1986 VW Jetta |
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