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Old 05-08-2012, 07:26 PM   #1
P5ylance
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Braking affecting RPMs

Curious. It might also probably be a symptom of an issue.

When I come to a stop, my RPMs sometimes dip. When I play with my brakes while at a stop (let off the brakes, then get back on the brakes) I see my tachometer needle bouncing. Sometimes, if I do it too much, then for damn sure my RPMs are gonna droppp... and stay low.

Now, I also recently changed all my pads, front and rear. I've got a really good bite for the first few hard brakes (I was testing it out today to finally seat my pads) and then it starts be aiiightt from then on. That's probably attributed to brake fade, but just something to mention.

My pedal goes kinda far in (i know its not like the family camry, where the brake pedal just kinda stops moving after you get so far), and if I wanted to i could give some extra force and press it all the way down the metal. Normal?

^now, this situation is on flat land. I tried this on my garage driveway (incline) and when I press the pedal in all the way, my RPMs begin to drop and do all that scary "im about to stall, please stop" business.

Anyways, the gist of this is: when I fiddle with my brakes, I'm able to get my car to feel like it's about to stall out. This doesn't seem normal to me, and it's also kinda scary when I'm at a complete stop for a long time and my car's shuddering like crazy (I end up holding the brakes, but keeping a foot on the throttle to open up the throttle body enough to let enough air in to keep my car from stalling... I could throw it in neutral, but the RPMs are still quite low). Also, when I'm reversing, my car sometimes shudders as well (after all this has gone down for a good portion of the day) and I need to give it some throttle to keep my RPMs up.

I am assuming it has something to do with a vaccuum leak somewhere (seeing as how it does things similar to symptoms of an FITV going out, except not as regular). Or if anyone may suggest, perhaps a brake cylinder needs to be replaced? I've already cleaned the IACV, and I'm most likely going to replace that pretty soon as well, just for kicks and to rule that out of the picture (I already cleaned it, and still suffering from problems)

so yeah, if anyone can chime in with knowledge, or if anyone has experienced these symptoms before and can pinpoint what exactly could be wrong, lmk. thanks everyone in advance who responds!
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Old 05-08-2012, 08:09 PM   #2
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This is just my theory, what I think is going on and I'm throwing it out there.

Your brakes also use engine power, and since your car is not moving and creating more power(adding RPM) it is more noticeable in the tachometer that you are using your brakes because some of that engine power is being diverted to your brakes, kind of like when the lights inside the car dim after turning on your headlights because it's splitting the power? I don't know but I believe this is it. I'd also like to see why this happens, I've noticed mine doing the same thing but I get no where near a stall.

Last edited by RedFalcoln; 05-08-2012 at 08:12 PM.
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Old 05-08-2012, 08:28 PM   #3
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perhaps a vacuum leak or dying brake booster or both. start the car, take a propane torch turn on the gas..but dont light it..and run the nozzle along lines and intake points you think might be a problem, if you hear the revs change up theres your leak. later
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Old 05-08-2012, 08:30 PM   #4
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Quote:
Originally Posted by RedFalcoln View Post
This is just my theory, what I think is going on and I'm throwing it out there.

Your brakes also use engine power, and since your car is not moving and creating more power(adding RPM) it is more noticeable in the tachometer that you are using your brakes because some of that engine power is being diverted to your brakes, kind of like when the lights inside the car dim after turning on your headlights because it's splitting the power? I don't know but I believe this is it. I'd also like to see why this happens, I've noticed mine doing the same thing but I get no where near a stall.


um..no.
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Old 05-08-2012, 08:35 PM   #5
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Both of you are on point, just wording it differently.

Our brake system uses engine vacuum assist. Sit at a stop light, pump your brakes, and your RPMs will rise.
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Old 05-08-2012, 08:57 PM   #6
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Both of you are on point, just wording it differently.

Our brake system uses engine vacuum assist. Sit at a stop light, pump your brakes, and your RPMs will rise.
seemed like he was taking the electrical draw route

In normal operation with up to par hoses etc you shouldnt notice that much of a rev change, but it will since the booster is consuming vacuum. Pumping the brakes shouldnt bog you to almost stalling.
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Old 05-08-2012, 09:15 PM   #7
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Thanks for the responses!

yeah, it gets ridiculously close to stalling. hits the last few tick marks on the tachometer in really serious cases.

So two possible things:

1) Brake Booster is going out... this is... the big spare tire looking thing on the driver's side firewall?

2) Vacuum leak somewhere, probably that bigger vacuum hose that comes out from the back of the IM plenum goes to the brake-y stuff area

I'm leaning more towards the brake booster then, or something that is definitely being used during times when my brakes are depressed. A vacuum leak would affect my car at other moments too, wouldn't it? My car runs exceptional, aside from a stop.
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Old 05-08-2012, 09:19 PM   #8
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Yeah, the brake booster is the big disc shaped thing on the firewall.

Pumping the brakes should cause the RPMs to rise slightly. If they dip dangerously low afterward, then it could be a number of things... vac leak, improper idle settings, possibly even issues with the IACV... or it could be a bad brake booster.

Check for leaks first. That's free... and vacuum hose is cheap. Replacing it wouldn't be a bad idea.
Find the threads by HondaFan81 that show you how to properly set your base idle and ignition timing. Do that.
Brake booster is next. I've seen failed boosters over 10 years ago, so if you're still running a 20+ year old brake booster, it's time. Even if it's not the main culprit!
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Old 05-08-2012, 09:44 PM   #9
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Quote:
Originally Posted by illinois_erik View Post

um..no.
But doesn't the brake booster use a vacuum from the engine to multiply the force that your foot applies to the master cylinder?
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Old 05-09-2012, 12:16 AM   #10
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I have experienced a similar issue myself. I'm not sure exactly what the problem was due to the fact that I replaced all the IM gaskets at the same time.

The first time I had these similar issues I started with adjusting the throttle body idle screw. Make sure you use some loctite. I didn't initially and the screw would back out by it self. I eventually ended up replacing the o ring on it and after setting the idle I coated it with grey RTV. Similar to OEM coating.

When I rebuilt my engine I purchased a complete Head gasket set and it came with any and every gasket and seal associated from the head all the way through to the throttle body. I went ahead and changed everything. I also had the IM off and went through pulling all the EGR plugs and cleaning out all the gunk in the ports. When I took apart the FIACV and IACV to replace the gasket they received a good cleaning as well. After all of that my motor ran really smooth again.

Oh I would also look into replacing the fuel filter if you haven't done so yet either.
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Old 05-09-2012, 01:18 AM   #11
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Thanks for the responses, Deev and Carlos!

For sure I will replace my IACV, since I have a spare. I've a feeling the IACV might not be properly controlling idle air flow, so since I have one I'm gonna replace it and then set my base idle to around 700-800RPM (my car feels more comfortable with it higher as opposed to the 600-700 recommended in HondaFan's guide) to rule that possibility out of the question. If it persists, then hoses, and then finally the brake booster i guess. I like getting new maintenance parts though, so that's a plus but i just paid for summer school tuition so its a stretch

This weekend or by next week after finals I should be able to get around to checking this, after that I will return with results to this thread!

Off Topic: Carlos, text me your number again my phone got flashed and I wants yo numbahh lol
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