tim.ocallag

My daughter has encountered twice where her 98 Honda Civic (in extremely hot weather and stop and go traffic) where her brake pedal can be pushed to the floor **AND** right after that the engine revs up high.
I couldn't figure out HOW they could be related but found there is a vacuum hose going to brake booster and I dont know much about cars but thought vacuum issues could cause engine racing? I tested the brake booster per the manual and it seemed ok (although it wasn't hot).
What could be going wrong when it gets really hot out and otherwise the car is fabulous. I had to swap cars with her so she woudn't be driving it.
This is REALLY weird !!
I have tested for vacuum leaks by spraying carburetor cleaner as the engine is running and did not identify any vacuum leaks.

I would really appreciate any suggestions on what might be wrong or how to troubleshoot.
Thanks in advance !!!

DO/\/\O

would also like to know... happen to a recent car i had..


i was told to bleed the brake system entirely

tim.ocallag

so now to sound like a dumbs**t ....after talking to the Honda dealer he prompted me to ask more questions of my daughter ..after doing so ..its sounding more like under the extreme heat the engine started racing and she just had to press harder on the brake to make it slow down. When she got the car stopped and put in park, the engine would race to 4K RPM. She turned car off and back on and the car still raced to high RPM. Only after sitting for a few hours, when she started it, it did not race.
So I dont think the brake pedal was going to the floor she just had to push much more to counteract the engine...
so the million dollar question is what would cause the engine to increase RPM in stop and go traffic when extremely hot (in fact that day the highway was buckling from the heat.
I'd like to change title from Hot Outside->brake pedal to floor->engine revs high to Hot Outside->engine revs-> hard to stop car with brakes but I don't know how.
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fleabag

check the floor mat and or remove it entirely. If that doesn't resolve it, then you need to take off the throttle body and clean it gently, not using any abrasive pads like the "green side of the sponge" etc. Just thoroughly clean the throttle body with q-tips, cotton swabs, cotton rags, and rubbing alcohol, actuate the throttle body and see how quietly and smoothly it opens and closes. Would not be surprised if the throttle body was getting stuck open. You can use some mild soap and water to clean it as well, though be careful because you could end up de-greasing certain parts that shouldn't be de-greased. You're mostly suppose to be trying to remove "gunk" from the PCV system which feeds into the intake.

DO/\/\O

^^^^ any write ups with pics?

pityocamptes

Could this be related to the temp coolant sensor and perhaps low coolant? I'm not sure if Honda has the same type of system, but I remember a vehicle I had that had a sensor in the water neck where it went into the block/thermostat - and when it got hot a few times the engine would rev really high. It ended up being a blocked thermostat and not enough coolant. How is your temperature when it gets hot? Any overflow? Might take a look at that, or maybe someone can chime in...

tim.ocallag

well, i finally experienced the issue personally..... it is definitely the engine slowly increasing in RPM (almost unnoticeable) and then you realize that you are pressing harder on the brake ..the difficulty in pressing the brake increases and you have to press harder to stop the vehicle....I switched the car to neutral and it raced to between 3000-3500 rpm. I tried kicking the gas to get it to go back down but that did not help. I switched off the air conditioning and that had no impact. I kept driving and putting in gear when I had to go forward, and neutral when I had to stop...it eventually subsided and went back to normal (maybe after 15 minutes)
Days before I had cleaned off any gunk on throttle body although it was pretty clean. Thanks for all the suggestions .....any other ideas ?

smooshies

The brake booster could be going out... although I have never heard of one going out in a random way like that, they usually either work or not. Is the brake fluid topped off?

Str8EJ

It really sounds like two issues.
The sinking brake pedal is almost certainly related to a bad master cylinder. When they start to go, I've found that bleeding the brakes tips a borderline m/c towards immediate failure, so I really doubt any advantages to bleeding the system. Hope that makes sense.

A bad booster typically makes the pedal feel too hard when the engine is running.

Can't explain the high revs. Is the engine check light on, per chance?

tim.ocallag

my apologies...the original title said brake went to floor ...turns out that is not the case ( i was interpretting what my daughter explained to me)....now that I've experienced it ...the ISSUE is that the engine idles higher in very hot temperature (2K-4K) and then you have to press harder on the brake to stop ...going to neutral makes the engine free rev up to the 2K-4K (normal idle is 1K)

Former User

Title edited.

Sounds like a bad brake booster.

PyroProblem

+1 on the booster.
Get something to clamp of the brake booster line. When the car starts revving up by itself, clamp down the brake booster line blocking all airflow to the engine. If the rpms settle back down, you found your problem.

kutilang

so anyone has any luck fixing this problem?

grumblemarc

iTrader: (4)

Did you check the brake booster?

tim.ocallag

i have done the brake booster tests (unfortunately NOT when the issue was happening) and it passed all of the tests.
I have the day off today and I'm hoping that it will recreate so I can try "clamping down the brake booster line blocking all airflow to the engine" to see if it has an effect.
The bad thing is this only happens in really hot weather ...not everyday.

DO/\/\O

problem fixed yet?

DO/\/\O

my car does the same dont know why

wile e

I know that this is an old post..just wanted to check in to see if you ever discovered the problem?

Thanks much!

crawfo661

its a bad brake booster, when it gets hot something weird happens with the diaphragm in the booster. it is sucking air from the cabin of the car where it attaches to the pedal assembly. thus creating a vacuum leak causing the rpm to rise. this could also be why the pedal is harder to push because you are loosing the vacuum assistance. Just my opinion, but i have seen it happen. OH Yea, and way to jack an old thread lol

tim.ocallag

well, I'm back.....
the car is 100 miles away and I will get it this weekend.
She said its happening more frequently and the outside temp doesnt even need to be as hot as before (75 vs 90+)
Always happens after 20 mins in stop and go traffic.
I'm hoping i can recreate and check booster while its failing.

One question I had....if I had a fancy OBD diagnostic system could I read out any sensor values,etc that will help me diagnose ? and is there ANY chance something like this
http://www.ebay.com/itm/ws/eBayISAPI...m=310678002251
would allow me to better diagnose ?
Thanks in advance !

MadVladCivic

How old is the brake fluid? As the brake fluid sits, it picks up
water from the atmosphere. This can lead to fluid fade in
stop/go driving esp during hot weather. You end up riding
the brake pedal to the floor as the water in the brake fluid
vaporizes in the brake line leading to compressibility issues.

tim.ocallag

Regarding last comment - I assume this was relative to brake pedal hard and not engine revs high ...right. My title is misleading and there appears to be no way to fix.
The issue really is engine revs high in stop and go traffic
Also, does anyone have any thoughts on whether a reading any sensor readings would be of benefit to diagnosing this problem >
THanks again
Tim

fleabag

It's simple guys: It's either throttle body/idle control sticking or it's a vacuum leak somewhere.

MIcL2WGq

I came to resurrect the thread because these exact symptoms happened to me. My case was different because I just changed the timing belt and thought I goofed something, but the timing marks were exactly what the instructions pointed too.

My car was sitting a few months before changed it, and as soon as I started it, the engine ran, what seemed like a wee bit high rpm, but after that warm up time it would almost stall then rev up to way above idle. I took it around the block and the engine was revving up like it would not stop.

I tried a bolt in the brake helper hose but that did not change the situation. So I looked into the Idle Air Control. It was gunked up with black soot, and even the little magnetic end was kind of tainted by some kind of aluminum looking corrosion. You know those white dots that show up on aluminum?

So, thanks for the advice on this post.

And this video showed me the simple fix in just a few minutes.

Honda Civic 1999 1.6 IACV- Idle Air Control Valve cleaning

My valve had a really rusted screw on one side of the plastic part where the electro-magnet thing is. Luckily I have one of those impact screw drivers that you can hit with a hammer to give a powerful force. If I did not have that, I would have been out of luck. It took me about 30 min in all to clean the valve real good with q-tips and gumout.