tim.ocallag

Could someone explain the operation of the 3 wire IAC valve and how I would test that it's working?

for example how does it open and close ?
can I do that by applying a specific voltage to a 2 wires,etc

I did look and found some info on the 2 wire model but nothing on the 3 wire model.

(I have a rotary 3 wire IAC valve on a 98 Civic)

Thanks

sleepyaccord96

rotary?

Former User

Is an IACV code thrown? If so, post it.

tim.ocallag

no fault codes ........I'm troubleshooting an engine that starts racing after 10-20 mins in stop and go traffic.
Last night, I removed and cleaned the IAC valve and checked the resistance from 1-2 and 2-3 (both about 21 ohms which is within range) but was curious how it works and whether I could make it open and close

Former User

No P0505 code?

Have you cleaned the throttle body and properly adjusted the throttle cable? It sounds like the throttle plate occasionally gets stuck open.

tim.ocallag

no code, I did clean the throttle body....but I need to figure out the procedure for adjusting the throttle cable...

question...when the car would race, I'd put into neutral and kick the gas pedal..to stop it but that never helped...would that typically un-stick the throttle cable ?

Former User

Is there about 1/2" of slack in the throttle cable? It should not be tight.

tim.ocallag

so I'm looking at the book and it says
Deflection 10-12mm (3/8-1/2")
does that mean I should be able to push down on the cable at the point of those arrows for 10-12mm without the throttle moving ?

Thx
Tim

tim.ocallag

so I checked it and it does seem about right.....
I also ran my engine with radiator cap off....and it appeared that some bubbles did come out but not much ...i hope if there was any air its gone.

I ordered a bluetooth OBD2 device so that I could read sensors on my laptop ... hoping that I could check things if it recreates... not sure what to look for but maybe temperature, throttle position,etc that might give a clue...

jdmh22eg2

well imo the air temp sensor will not cause a surg. have you gone around the engine to ALL the vacuum lines with carb/brake clean when it does start racing? i have seen on some late model gm's (gm tech here) when the engine bay gets over certain temp it opens a vacuum leak that is not present when cold and causes engine to surg

tim.ocallag

thanks for the idea... I will try that ...of course the darn thing happens only once every 7-10 days....
I will try just the brake cleaner with the engine tonight (although its not acting up) and see if I find anything.
Being an engineer I like to understand how things work....so why does vacuum leak cause engine to surg and does a vacuum leak anywhere cause the same issues or does it depend where ?

tim.ocallag

well, not while its failing but while engine running I checked some random things

1. sprayed brake cleaner all over and no change
2. blocked lower port in throttle body and engine slowed down (normal)
3. checked brake booster hose for vacuum (ok)

argg...I need to drive around in stop and go and see if I can recreate tomorrow...

MJ 95 del sol

ive read on a few other sites that it could also be a coolant level issue either to high or to low.. if to high radiator doesnt have room to vent and breathe but, to low makes it overheat and rev.

MJ 95 del sol

had the same thing happen to my 95 sol about a month ago changed every gasket from the head up plus timing belt and water pump but it continued revving, got to looking yesterday had a cracked radiator

tim.ocallag

interesting....
so with a cracked radiator..were you loosing coolant and the car overheated ?

This is my daughter's car and it always happens in stop and go traffic when hot out....but she said that the engine guage is at 1/3 (normal spot) every time it happened except for 2 times and the engine temp gets hot after a while of her pressing the brake so she doesn't slam into the guy in front.
I told her to put in neutral when she has to stop but she didn't follow that advice and just pushed on brake..thus I don't know what rpm it was racing at.
She did say that if she took her foot off of the brake the car would reach 45mph pretty quickly with no gas pedal pressed.
She also said that she normally has the A/C on, but when it starts acting up she turns off A/C but that does not help.

Former User

This^ problem is just as concerning as the high engine revving. Does the radiator fan run when the engine get hot?

Given the high engine rpms required to do this^ and the absence of a CEL, I still think that the throttle plate or throttle cable is getting stuck.

You might consider replacing the throttle cable and re-cleaning the throttle body.

Or is the floor mat possibly shifting and holding the throttle pedal down? There's a metal peg that acts as a safety device by inserting into a hole in the driver's floor mat to prevent this from happening.

tim.ocallag

Thanks for the input !

FAN - wish I knew..... will need to check next time it acts up

Throttle cable- I will reclean the throttle body ....but wouldnt the kicking the gas pedal "unstick" that ?

Floor Mat - I'm sure not.

Former User

Possibly not in all cases.

tim.ocallag

so another question...if it happens again...and the throttle is sticking...if you remove the air filter you should be able to see the throttle plate in the open position or closed position (to cause the engine racing)...just want to make sure what exactly to look for to confirm one way or another

tim.ocallag

so... i got the engine to act up.... normal idle is about 1K rpm when at stand still, after simulating stop and go traffic for 30 mins on a country road, I could hear the engine start to work harder....when I put the trans in neutral the rpm went to 2500 rpm.
I then took off the air cleaner to look at the throttle and the butterfly valve was shut, I also checked and the radiator and AC fans were both running. Note the temp gauge never moved and was at 1/3 (normal).
The only thing was I forgot brake cleaner to check for vacuum leaks but I need to ask....with an engine that's pretty hot, is it safe to spray brake cleaner on ?
Also, since butterfly was closed does that rule out the throttle ?
Any other ideas ?
Thanks

blomer

Title is "explain 3 wire iac valve" but the thread moved on to other things. I don't see the iac being explained...
I really need to know how this 3 wire iac valve operates, what each wire is doing.

I drive a 96 Civic LX manual transmission, engine D16Y7

My IAC makes a buzzing sound with KOEO. I replaced the ECU, still buzzes. I really want to know how to check the wiring, thinking I have a short or something, but don't want to test things the wrong way and fry something else.

mk378

A buzzing sound is likely normal, it being an electromechanical device. Does the car start, idle, and drive OK? If so, you're overthinking it.

The three wire valve has two solenoid coils inside. One pulls the valve open and one pulls it toward closed. The ECU drives one or the other coil as needed.

This is in contrast to the two-wire valve that only has one coil. A spring pulls the two-wire valves closed when the coil is off. The ECU drives the coil with a variable amount of electricity to open the valve.