set idle via IAC valve

mike1978 · Posted: Tue May 27, 2008 9:39 am Post subject: set idle via IAC valve

Hi,

Does anyone know how to set the IAC valve up? i`ve loosened the 2 screws on it and can rotate it.

Basically, once the engine is warm, when i come to a junction the engine will stall unless i keep the blipping the throttle.

I`ve tried 3 different valves with not much luck. When i adjust the valve, the rpm will raise or lower depending which direction i move it in, but then the rpm readjusts itself (i guess this is the ecu compensating) to around 800rpm.

I`ve got a bit of difficulty setting it at the moment as i don`t have a rev counter fitted and am doing it by ear.

thanks,
mike

rjes · Posted: Tue May 27, 2008 3:39 pm Post subject:

Hello Mike,
I'd be certain thet the idle speed control is a closed loop negative feedback system - i.e. the ECU has a target rpm (something like 800 when cold and 600 when hot). As the revs go above the target, the ECU will reduce things until they drop, and vice versa. Therefore the ECU will compensate for anything which causes a rpm change, within reason. By moving the valve I imagine you are altering the balance of adjusting above / below the target rpm that the ECU can do (because the valve will run out of travel sooner one way, and vice versa), but not altering the target.
To add to the complication, I have just discovered that the coolant temperature compensation is done mecahanically at idle, not electronically. The base of the IAC valve has a bimetallic strip in it, heated by the coolant flowing through the two 8mm pipe fittings. This strip turns a second shaft and valve, so the IAC valve assembly is effectively two valves in one. I would have pasted all the details in here, but they're images. I've e-mailed them to you.

The Subaru service manuals only cover replacement of the entire valve, not how to set the electronic actuator. They don't expect you to take them to pieces. Their recommended procedure for cleaning the valve is to pour a special cleaning solvent in with the engine running over 2000 rpm. Never heard of it before.

Is your engine temperature sensor definitely plugged in (the one with a 2 pin connector, not the single pin one) - they are very easy to forget to plug in, and definitely play a part in the idle speed control system, as well as the above mechanical system. I also e-mailed you the info on what inputs effect the idle control system, and the whole diagnostic section on the IAC valve.

Also e-mailed is the procedure for setting the throttle position sensor. My previous guess was very close. Basically, set the sensor so it's output is 0.5 +/- 0.3V at idle, and 4.3 +/- 0.5V at full throttle.
Anyone else - note this applies to the MY95-MY99 throttle position sensors with three connections. Earlier ones with 4 connections are likely to have a different procedure.
_________________
Regards,

Richard,

R J Engineered Solutions
Quality Subaru Powered VW Components
www.rjes.com

mike1978 · Posted: Tue May 27, 2008 4:28 pm Post subject:

hi richard,
thanks for the info - i thought that the ecu was probably compensating as you can hear if the revs are too high, it`ll suddenly drop it or if too low, it will suddenly raise them.

the 2 pin plug you`re talking about - is that the one that connects on top of the expansion tank? if, so that is definitely plugged in.

i guess, its just going to be a bit of trial and error - i`ll recheck the throttle position sensor.

By the way - i did`nt get the emails - the correct email address is -

'emailmikesmith at gmail.com'

Thanks,
Mike

ElusiveStranger · Posted: Tue May 27, 2008 5:27 pm Post subject:

The temp sensor Rich is talking about it the two pinned brown one on the water manifold. If this ceases to function it will activate the ECU controlled fan.
Disconnect it and key on, engine off. Fan should come on after a second or so

I do get a code 24 (IAC) from my ECU but it only happens when the engine gets to temperature. It doesn't affect my idle so I don't worry about it.

I'm wondering if a PO has set the idle speed by adjusting the TB stop...you've then tried to adjust it properly but the IAC can't set it properly due to the TB adjustment being incorrect. This is only my thoughts.
I'm sure the butterfly is totally closed at no-throttle.
_________________
The advice you receive on here is worth the paper it's written on.
Your experiences are worth shed loads to others, including the f'ups - live and learn.
Wouldn't YOU rather learn by someone else's mistakes? So would they.

'78 Bay, 2 litre 091 box, EJ20 NA & the ashtray's on the 'right' side.
I don't lean forward for hills any more Grin

Bugger, missed out on "Live fast, die young"

mike1978 · Posted: Tue May 27, 2008 5:42 pm Post subject:

is there a procedure for setting the throttle stop for the butterfly. i have`nt touched this since i got the engine. should it be very slightly open?

ElusiveStranger · Posted: Tue May 27, 2008 5:56 pm Post subject:

http://www.weidefamily.net/vanagon/HTML/05/05/08/01.html

I knew I'd read it somewhere and couldn't remember where
_________________
The advice you receive on here is worth the paper it's written on.
Your experiences are worth shed loads to others, including the f'ups - live and learn.
Wouldn't YOU rather learn by someone else's mistakes? So would they.

'78 Bay, 2 litre 091 box, EJ20 NA & the ashtray's on the 'right' side.
I don't lean forward for hills any more Grin

Bugger, missed out on "Live fast, die young"

mike1978 · Posted: Tue May 27, 2008 7:40 pm Post subject:

thanks for the link - thats what i`ve been pretty much doing. i`ll have a proper few test drives again tomorrow night or the night after. the thing is , you adjust the idle like that and then before you know it, the ecu readjusts it to 600-800rpm!

i checked the temp connector on the manifold and when i disconnected it and tried the ignition, the fan came on and when connected didn`t so i guess thats ok.

i also had a look down at the throttle butterfly. the screw is marked with red paint and the mechanism stops on the screw when closed. i had a look down the intake and the butterfly looks like its probably open a tiny tiny bit but was hard to tell as its a bit gummed up round there - could do with a clean.

rjes · Posted: Tue May 27, 2008 8:46 pm Post subject:

Hello Mike,
I found a lot of info on the injection system in general today on a Subaru service CD. I tried (and so far failed - but have not given up yet!) to e-mail all the relevant bits to you. It makes no mention anywhere about adjusting the idle speed control valve, so there is no procedure to follow.
What was interesting is the proper cleaning procedure. You are supposed to pour in a special cleaning solution into the valve with the engine running over 2000 rpm, which apparently makes a lot of white smoke. I'm not sure I'd dare pour liquid into a running engine's intake!
_________________
Regards,

Richard,

R J Engineered Solutions
Quality Subaru Powered VW Components
www.rjes.com

ElusiveStranger · Posted: Tue May 27, 2008 10:24 pm Post subject:

I've been scouring my CD too (I think Rich's is the same Wink

) and can't find any adjustment guff at all. Does look like you just put the IAC back in *shrug*
ECU must just take cam/crank rpm and alter the injector & IAC ratio to suit.

I think the cleaner's called Seafoam. I just stripped & blasted mine with carb cleaner

I'll whip off my intake tomorrow night, weather permitting & let you know how the TB butterfly sits.
_________________
The advice you receive on here is worth the paper it's written on.
Your experiences are worth shed loads to others, including the f'ups - live and learn.
Wouldn't YOU rather learn by someone else's mistakes? So would they.

'78 Bay, 2 litre 091 box, EJ20 NA & the ashtray's on the 'right' side.
I don't lean forward for hills any more Grin

Bugger, missed out on "Live fast, die young"

rjes · Posted: Tue May 27, 2008 10:30 pm Post subject:

Mike's description of how the throttle sits sounded right to me. They generally stop as close to being fully closed as possible without jamming up. I would guess that there is maybe just a few thou clearance.

Mike - the mail seems to have (finally) sent OK now. I'm getting very annoyed with my 'new' wireless network adaptor. It's crap! I had to hard wire the laptop into the network to get your mail to send without the wireless giving up half way through.
_________________
Regards,

Richard,

R J Engineered Solutions
Quality Subaru Powered VW Components
www.rjes.com

mike1978 · Posted: Wed May 28, 2008 8:19 am Post subject:

thanks guys - ES - if you could check how your throttle butterfly sits that `d be great Wink

rich - i finally got your email - will have a read through them today. i`m going to try having a play with it tonight. i`m loathe to try to adjusting the throttle stop at the moment as everything i`ve read seems to say don`t go anywhere near it!

i`ve just cleaned them with carb cleaner at the mo - i`ve actually got 3 different IAC`s (!) - the original, and 2 spares from '98 cars. i think i may double check the throttle position sensor voltage tongiht aswell again.

mike1978 · Posted: Fri May 30, 2008 7:36 am Post subject:

well, i had a play with that valve last night and adjusted it so that when the revs drop, they don`t drop below 500rpm then recover to about 700. they just drop to approx 600rpm and stay there.

I drove 20 miles this morning into work (longest drive yet!) and it didn`t stall when coming to a stop anymore - seemed a bit happier Happy

the only thing is that at one point after about 15mins driving at about 60mph, a car pulled out in front of me - i dropped from 5th to 4th gear and the error light came on. i checked it when i got to work and it was that damn 24 again(!)

the van seems to run fine - i`m still not sure if i`m getting the over 4500 rpm without a rev counter- should have one of those in abotu a week or so.