Redprelude98

well i think i might have a vacuum leak in my brake booster or something because say when i am at a light if i press on my brake pedal like 5 times my idle starts jumping and goes from like 1000 rpms to 1600 rpms and this is what i think it is and also it starts doing it after i have been driving and have to come to a stop like kind of fast, if this is what the problem is how difficult is it to find out where it is and how to fix it?

92ehatch

if you pump the brake light that it will make the idle fluctuate slightly.

if the brake booster was not working correctly the pedal would get harder to push

Redprelude98

yeah when i pump my brake pedal it stays the same and the idle goes up and then when i let off it starts that wierd thing as if i have a bad iacv

Redprelude98

anyone know?

Redprelude98

does anyone have any clue please people?

macson

The idle will bounce between 1k and 1.6k if you come to a quick stop/after you've driven a while? Does it continuously jump or does it mainly stick at an RPM in that range? Either way, I don't think checking your IACV and all vacuum lines would hurt. I've even seen bad PCV's cause weird vacuum/idle issues.

Redprelude98

i unplugged the iacv and the idle dropped really low and then i plugged it back in and it was fine...but you see it continuously jumps and as i said before even if i just start the car and drive around the block and then when i come back if i pump the brake pedal my idle goes up like over 2k and then drops back down to like 800 and then jumps and goes from 1000 to 1600 and i really cant find a diagram of all the vacuum lines, is there anyone that knows where i can find one? i will have to check the pcv tomorrow because it is raining outside and it is kind of dark

Redprelude98

is there anyone that can help the pcv is good

Former User

Try these tests:

Former User

Here's something else to look into:

Redprelude98

so i checked that brake booster vacuum hose and when i went to oreilleys they said they didnt have a vacuum hose with that valve thing built in so they gave me a piece of just vacuum hose will that work? or do i need the one with the valve thing inside?

Former User

You need the check valve.

Redprelude98

ok well i put the old one back on because i just figured why not to see what happened and i put some better clamps on it and now the brake thing is back to normanl but now when it starts idleing wierd and going up and down and up and down if i pull the tps sensor it keeps doing it but if i pull the iacv then the idle drops and if i pull the map sensor it just dies....so could that mean either that i have a bad tps sensor or maybe a loose wire within the tps sensor well the wiring going to it?

Former User

I the CEL ON?

Now try cleaning the IACV, looking for another vacuum/intake air leak, and bleeding the cooling system.

Redprelude98

no there is not a cel on and how do i clean the iacv and also how do i bleed the cooling system? i have sprayed carb cleaner on every vacuum hose i can find and it did nothing

Former User

Cleaning the IACV is described here.

To bleed the cooling system, turn the dash heater **** to MAX heat and then do this:

(Parking the car on an inclined driveway with the front end up will help the bleeding process.)

Redprelude98

ok so i tried this and it still does the wierd idle thing and i have like run out of things to do...anyone else have any ideas and no there are no cels on

Former User

You may need a new IACV.

Redprelude98

damn...even though when the car is started when i unplug it the idle drops really low and almost dies and then when i plug it back in it goes back to how it was

Former User

I think it's wise to focus on the IACV because, although unplugging it drops the idle speed, it stops the idle surging.

Redprelude98

true yeah i will see if i can find one and then i will let you all know what happens...thank you sir i appreciate your help

dly91

did you figure out if the iacv was the problem? bc my civic does the exact same..

Lenman1

Still no answer to this I'm having the same issue except I changed my iac and tps and map sen. And my brake pedal is very spongy even after bleeding them

oSrBo

RonJ@HT I Summon Theeee
So im having the Same exact problem as this kid but i have a b16a. Swapped into a 94 hatch.
Ok So the Throttle body has No FiTv im wondering if that will constantly cause an idle issue. Im gonna run some test soon an Hope you see this post Hahahaha Gotta get this idle fixed!!!! and my Brakes! i dont wana die in a car wreck :-/

D'PEXi

I've been fighting idling problems for a long time, but I think this might help you.

Keeping in mind that you have no vacuum leaks or a faulty fast idle thermal valve (FITV), or some random sensor.

Turn your car on to warm it up to operating temperature.

When the bouncing idle happens, pull the harness plug on the idle air control valve (IACV).
1) The idle drops to normal and should be steady.
2) If it idles steady at a high RPM, turn the idle adjustment screw, located on the throttle body, clockwise to tighten it. Adjust your idle to your car's spec via a manual (usually 400RPM - 550RPM).
3) If the idles drops abnormally low and is steady, or engine dies, turn the idle adjustment screw counter-clockwise to loosen it. Adjust your idle to your car's spec via a manual (usually 400RPM - 550RPM).

Turn your car off, and connect the IACV plug.

Undo the negative cable from your battery, and leave it off for a minute. This will reset the ECU. If you have an ECU fuse in one of your fuse boxes, unplug that instead and leave it off for a minute. This will save you from having to reset your clock and radio, etc.

Relearn the ECU
Make sure your e-brake is up, step on the brake and turn on your car. Release brake pedal, and don't touch anything. Make sure your headlights are off, heater is off, wipers are off, defroster is off, etc. You want the car to be under NO LOAD conditions. Let the car idle for a minute until it warms up.

Then turn on your headlights (lowbeam, not highbeam), and your heater fan to max. Let it idle for another minute or two. You may take it for a short drive if you want to.


If your idle continues to bounce when warm, then you have a bad IACV.
You can try cleaning the IACV with brake cleaner, but best results happen if you remove it to clean. There have been many write ups on the internet.

You may want to invest in a $4 IACV gasket from Honda for your specific year IACV, as the original ones have probably been flatten.

Replacement IACV units from Honda are over $200, so sourcing one out at the local wrecker would probably be best if you decide that you need a new one.

Hope this helps you.