Honda IACV explained

[cnc]

WARNING
Long post. If I wrote someting incorrect, straighten me please.

For quick info go to Chapter 2.

Chapter 1.

Some time ago I had iddle issue. 93' Civic VX, 250000km.
Briefly:
- cleaned EACV
- adjusted iddle
but the real couse was Purge Control Selenoid Valve (PCS) vacuum pipe was cut a bit, PCS had oslo some small crack causing air leak. Constant vacum control valve (CVC) had some crack hidden close to manifold vacuum pipe (someone had to pull the pipe causing crack or someting).

After some time the iddle problems came back to me .
I started digging forums again and I've found a lot of useful info and long stories about iddle issues. Every case looks a bit different so I'm pretty far away from saying "check this and that, it will fix you problem" but I'd like to share some thoughts and observations.

Temp went down from 15'C to 2'C (arround -5'C at night) during last weeks. After starting 1500rpm's - acceptable, no fluctuations. Once it got warm iddle went down to about 600rpm's. When I stopped on lights the iddle fluctuations appear (from arround 400rpm to 1100rpm) . I always try to think what has changed:
-maybe some valves got dirty too much to work as before
-maybe some sensor died
-outside temp. went down

Chapter 2.

Again I've checked all the piping for vacuum leaks - no leaks . I looked at vacuum diagrams for long time, I even created some kind of Ishikawa diagram . I knew my Electronic Air Control Valve (EACV or EAC) called sometimes Idle Air Control Valve (IACV or IAC) is clean, PCS and CVC is repaired, i don't have vacuum leaks for this part of the system. I went to other parts of the VX system. I've read about PCV valve which is located deep under intake manifold. I took a look (it's not easy to find it for the first time) and reach it with pliers. PCV was clogged (which seems like common problem) but I noticed PCV rubber is very hard (can't blame 93' car) and there were oil leakages arround the PCV hole. I've cleaned PCV and decided to swap hollow elbow with PCV, put new long pipe from elbow to PCV. Hollow elbow rubber was also hard so I had to use some thin sticky rubber tape to seal it. The best way would be to change all rubber parts for sure (that's the plan). Last thing was iddle adjustment (standard well known precedure: engine on, unplug EACV, make short circuit on diagnostic plug, adjust screw on TB (set iddle - fot VX 420 +/-50 rpm), turn the engine off, unplug short circuit on diagnostic plug, plug in EACV, take out back-up fuse for a minute, wait to cool down, start engine, wait until the radiator fan starts, take a ride).

So far it works but what makes me think is the rubber parts and vacuum leaks. They are also crucial for the iddle issues and pretty "cheap" and easy to verify at the first place. I could change plugs, wiring, check grounding, clean TB, change ECU, try to adjust iddle etc. without any success.

Chapter 3.

I totaly agree that sensors fail, good ground is crucial for all electrical devices, welds are important, vibrations can wear down the wiring insulation.
Although I think at the beginning it's worth to remember what is the sytem based on - air, electrical signals, rubber, plastic, metal etc. As we all know most of the holes made in engines (e.g. aluminum alloy) are getting bigger while hot. Rubber could get more flexible but it's not expanding like aluminum alloy.

Everytime I'm looking for causes of failure I try:
- start from basic things (like is there vacuum, power etc. at all)
- to go back (step by step),
- think what has changed,
- when exactly it started,
- what was the exact situation,
- who was fixing IT (who? how? where? when? with what?)
- how all of this could influcence my problem

Unfortunately lots of failures appear as resultant of different small failures and that's why they are so hard to solve. The only way is to trace them separately and try to eliminate them each after another.

The End - sorry for long post.
I'm also sorry if I sound like I knew more than I know

Thank you to all who shares the knowledge - I would be in dark forest now without YOU!
I wish you all patience and time.

[RatherDashing]

Originally Posted by bengry

bumping this from the dead.

I have a VX engine D15Z1 i am working on getting into an 89 civic wagon.

I do not have a IAC valve. Is the IACV very specific for a vx?

I see that the vx does not have the fast idle thermovalve. It does have a bolt pattern similar to the one shown in image 23-8 shown above. I am thinking about going to a yard and finding something with a similar bolt pattern and 2 wire plug.

Any one else run into an issue replacing the IACV on a vx?

iv got a 94 vx with the d15z1. i just managed to get mine off right now since all the symptoms that I am having aim straight towards the valve. im hoping this throughcleaning takes care of it otherwise its a 150$ part. its right behind the intake manifold held on by two bolts

[rustycrx]

Ok I dug into how the the three wire IAVC works. It appears that the third wire on the IAVC is a solenoid that closes the valve. Basically it replaces the spring in the two wire version. It is just the inverted signal of the other. So lets say if the signal on wire one is on for 1 second and off for 2 seconds then the signal on the wire 3 is on for 2 seconds and off for 1 second (you would never see pmw like this but its a example). So if you my guess is that if invert the signal on 1 and applied it to 3 (not sure which wire is common) you should get this value to work. So slap on a PWM inverter on wire 3 and walla... 2 wire signal controlling a three wire IAVC. This is just a educated guess but is anyone up to trying this out? I am still waiting for my motor so it could be awhile before I can try this. I am will dig around on Newark for some thing that should work.

[RatherDashing]

Im debating on buying a new iacv.the reason for my idle not dropping normally was the tps was wayyyy off on the calibration. 1.45 at closed throttle. Now the iddle fluctuates up and down a little over 1k rpms but stops at a complete stop.iv taken it out and cleaned it several times.my radiator is leaking .cud off coolant pressure thru the iacv cause wierd idling issues as well?

[Cobb]

What can you tell us about i-VTEC and i-Dsi? I swear under certain conditions it feels like its running on 2 vs 4 cylinders.

[RatherDashing]

Seafoam deep creep got a lot of gunk out of my iacv.
First make sure the gasket is good and the filter is clean.spray brake cleaner like crazy in it and let it dry out.then spray some seafoam deep creep in there and let it sit for a while.recleaned it out again and got a lot more gunky black build up.also running seafoam thru the brake booster vacuum line every so often has been keeping it clean as well.last resort you should ever have to buy a new one if these don't work

[nobrush]

Did I miss something for the 3 wire IAC valves? 23.4 States "The 3-wire IAC valve is covered at the end to this section." but I don't see how to test it or any info for it. I'm working on a 2003 Honda Element and just want to make sure it works or not (i.e. ohm/voltage reading on which pin). I did see in another post that the 3 pin is like the two pin plus the 3rd wire acts as the spring. I do have the manual for the car but it just states to do a IACV test on the Honda brand OBD II sensor and I just have an off brand one.