I have some issues with my zc that i would absolutely love to resolve, and i think they all point to maybe one thing:

1. when i get off the throttle, the motor dips down past idle, shakes a bit, then returns to idle.
2. i have a slight misfire, especially when its cold.
3. the throttle isn't very linear... it feels like its contantly changing just slightly, so i can't really get super used to how the motor will react to my right foot.
4. i adjusted my idle to the highest setting, and its still pretty low, maybe around 600 rpm according to my tach.

I am thinking that these could point to a vacuum leak, but i can't find it. I tried spraying carb/injector cleaner, but i couldn't notice any change in the idle... so i really don't know. Maybe i have a bad o2 sensor? i'm just guessing... does anyone have any ideas? just throw it out there, suggestions are much appreciated.

Also i have tried on several occasions to remove the idle valve and clean it up, as well as cleaning out my throttle body. this seemed to help a bit, but not really solve it. I've also set and reset ignition timing, the tps sensor, swapped distributors and spark plugs... thanks everyone for your help!

 

yah check your idle sensor...?

 

Might have a look at the cam(s), crankshaft pully alignment. Make sure the pully is aligned along with the cam(s).

Or take a look at your fuel pressure regulator. It may have gone bad allowing to much fuel pressure to build-up, causing a rich condition.

A vacuum leak on a Honda, tends to create a uncontrollable idle speed, rather then what you have mentioned. The MAP sensor will see that more air is entering the system. Then telling the ECU it needs to increase the injector pulse width to compensate for it.

Just some thoughts....

 

With the idle dipping really low I have the same problem with my ZC if it rains the night before it will do that. What ECU are you using I heard people with the Teg ecu have this problem. I never had this problem till I went turbo, on rare occasions the car will stall on me, but once it warms up its fine.

 

hmm, unless my timing belt has slipped a tooth, i am pretty sure that my cam and crank pulley are properly aligned, but i shall double check that. FPR huh? i that did not cross my mind, i'll have a look into that as well. Also, I'm using the ZC ecu... Thanks for the replies! keep them coming!

 

oh, and does anyone know fpr compatibility? can i use any from a d-series (maybe from my stock engine?) or do i need the integra one? or perhaps aftermarket? thanks!!

 

i had a simaler prob with my car but it ended up being a vacuum leak

 

IAC- Idle Air Controll, it keeps your engine from dipping when decelerating engine speed, are you throwing any cel's?

I'm not quite sure how you go about checking the IAC, but i do know there is a way...

 

I've removed and cleaned out the IACV on my ZC as well and the idle drop only improved a little. I'm thinking the valve actuator just may not be working well. I tried to stroke it ( get your minds out of the gutter) by using 2 C batteries on the terminals, but I had to use a 9v battery to get full movement. I think this thing is supposed to be full open at 4 volts, so mine may be dying.

 

...did you do the idle adjustment with the idle control valve connector disconnected?

 

i've been having almost the same problem, so i'm interested what helps you. keep us updated!

 

oh yeah, the classic ZC crappy idle problem. Mine has a similar condition; it seems to idle great when its not fully warmed,
but once it is it idles at whatever the idle set screw is set to. This means that the EACV is not working properly, which I
have confirmed by disconnecting it while the engine is running at a normal warm temperature. When the EACV is unplugged,
the idle should drop a couple of hundred, to about 650 RPM (factory setting). When I unplug my EACV, nothing happens. It
actually works briefly if I pop the plug in and out quickly, but that's it. It also seems to idle fine for a few seconds after coming to
a stop, but then dips. This all seems to point to a bad EACV, but I have had the same results with 3 different units. I can't spot
any vacuum leaks (anybody have a good method for finding them??), so I am starting to think that the ECU is faulty. As well,
is the D16A6 EACV the same as the stock JDM ZC one?

good luck

 

yes, i'd also like to know about EACV compatibility. its pissing me off enough that i'm willing to go buy a new one and try it out...

yeah, and i guess its technically called a EACV before '92, and an IACV afterwards..

https://honda-tech.com/zerothread?id=312714

Here's a thought i hadn't considered until just now: i did the throttle body coolant bypass thing.. maybe that has to do with it. I'll run it with coolant soon and see if that helps.

 

Same thing with me... No vacuum leaks, nothing. My TPS wire popped off, and it was causing me to stall. I plugged it back in, and now I just have the choppy idle. PG7 for me...

jB

 

gregv:

bad EACV or bad connectors? when you come to a stop, maybe the rocking motion of the engine will momentarily make and then break connection... just a thought of a potentially easy fix, if that...

 

ad its a damn good thought at that! I will check it out this weekend, as well as doing the "misting water
to look for vacuum leaks" trick.

cheers

 

well, today I took off my throttle body and eacv, and cleaned them up, and i am also now running coolant through my throttle body again. the idle dip has improved only slightly... so, i don't know. one thing I found out that was interesting is, the idle dip is way way less severe with the eacv unplugged! i'm not sure why.. but i think i'll try replacing it... i guess with a d16a6? unless anyone knows for sure which one is compatible..

 

when i unplug my iacv it dies....is it suppossed to keep running?

 

um, mine still runs with it unplugged...

just now, i pulled off my throttle body again, because i guess yesterday when i put it back on i developed a vacuum leak.. oops.

but, i was looking at it, and found an adjustment for a throttle stop. its on the bottom of the throttle body, and basically impossible to see unless you take it off. it consists of a nut on a stud that accepts a hex key or allen wrench. there's paint on it to mark its original position.. but i tinkered with it anyway. i was able to raise my idle doing this. previously, i could only adjust my idle up to around 600 rpm using the adjustment screw on the throttle body, so i count this as a small improvement... i still get the idle dip though..

 

The basic idle speed is set with the EACV disconnected. It should be about 500-600rpm. When you connect the EACV, the idle speed should increase to 700-800rpm. This preset bleed allows the EACV to keep the engine running when the engine is quickly decelerating. If the preset bleed is not large enough, the EACV may not open quickly enough to keep the engine from stalling.

You should not have to adjust the throttle stop screw you mentioned, unless, as you've described, you cannot get the engine to idle with the idle screw on the top of the throttle body. You might try backing the idle screw out all the way and shoot some carb cleaner in the hole to clear away anything that might cause an obstruction.