IAC Woes...

TomsSVX · #1 10-07-2007, 04:33 PM

Ok, I have had idle issues with the stage 3 ever since I got it.... I had it idling nice for a long time.... BUT it wasn't proper. After I installed my wideband, everything came to light. My idle was high but then would inadvertantly drop. This drop i found later was due to a fuel cut as when it would happen, my AFR would drop off the map. I toyed around with using the high idle controler and not. I have also toyed around with the wiring to the ECU by jump the neutral pin to ground... None of these are helping me at all.

Right now, all the air leaks are sealed.

The IAC is cranked all the way up so the car won't stall as soon as I let off the gas.

It'll idle decent but as soon as I turn off the car and start it again, the idle will jump to 1500-2000rpm from 1k I had it at earlier. If I adjust it back to 1k, it'll drop again and end up stalling the car after I drive the car for a few seconds... Really starting to piss me off BIG time and I could really use some other opinions as I am running out of patience.

Tom

SomethingElse · #2 10-07-2007, 04:44 PM

I may be way off but is there some kind of parameter the ecm learns when the car is first started? If you kill swich the battery beetween startups would it change?

TomsSVX · #3 10-07-2007, 04:55 PM

no, disconnecting the battery was no use... I also thought it was a learned procedure but after 150 miles with several starts.... you woulda thought it would learn something right?? Nope... still ****

Tom

UPnorth362 · #4 10-07-2007, 06:09 PM

Just wondering if you have checked to see if you have consistent manifold and T/B vacuum before the S/C. where do you get the vacuum for the IAC, before the S/C? With that S/C making different amounts of vacuum behind the T/B, it might be hard to get the IAC to adjust properly at idle, because of different amounts of vacume being applied from S/C surge. Maby a electronic vacuum booster is in order? Do you have a good vacuum gauge hooked up to monitor any differences.
Just a thought.

TomsSVX · #5 10-07-2007, 06:34 PM

only vac gauge is hooked up to the manifold so its post s/c. I do notice that it idles well when vac is up but when idle drops the vac drops. It may simply be that I do need a vac pump b/c I only make 15 inhg at idle

Tom

porschekiller · #6 10-07-2007, 07:16 PM

the only time i had the same problem was when i switched the cam in my 240sx, so maybe timing. if it's any consolation i'll have a set of stock wheels and tires for you to keep. check your email. you'll need sleeping bags.

Trevor · #7 10-07-2007, 10:18 PM

Quote:

Originally Posted by TomsSVX

The IAC is cranked all the way up so the car won't stall as soon as I let off the gas.

It'll idle decent but as soon as I turn off the car and start it again, the idle will jump to 1500-2000rpm from 1k I had it at earlier. If I adjust it back to 1k, it'll drop again and end up stalling the car after I drive the car for a few seconds... Really starting to piss me off BIG time and I could really use some other opinions as I am running out of patience.

Tom

Tom, looks like you have a curly one.

I am not exactly clear as to your set up, particularly as to whether you have retained the original inlet manifold, with the Bypass Solenoid Valve and Auxiliary Air Control Valve remaining without modification.

Thinking alongside you, the obvious items to consider are the BPSV and the AACV. A signal from the ECU controls both of these, but the AACV will be slow to respond, as it heater'/bimetal in operation and this arrangement must have been selected for a purpose.

It is difficult to ascertain the exact mode of operation in respect of the AACV, but one would assume that heat would result in the shut off of air; i.e. heat from the engine, or heat when the electrical element is energised. This instigates thought as to whether any modification has resulted in a lack of direct heat conduction from the engine.

My suggestion in any event, would be to open and close the throughput of air in respect of each valve, observe and contemplate. The result should throw up information as to which idle air passage should be adjusted/modified. My point being is an electrical signal involved, or simply direct heat/cooling in respect of the AACV ?

Deeply involved, you may have passed over considering the possibility of a component fault. The cut and try procedure as above, could also throw light on this as a possibility.

Be sure that I am not trying to tell you how to suck eggs, but rather am trying to put in place a possible alternative line of thought.

Meantime, "what a bugger"

Trevor.

TomsSVX · #8 10-08-2007, 10:01 AM

yeah, its def a pain in the ass

Now I need to know what you mean by aacv (aux air control valve?) then what do you mean by bypass control valve??

The USDM svxis run on 2 main idle air control valves. One beign the aux air control valve... commonly known as the cold air idle controller. This is a seperate solenoid under the driver's side of the intake maninfold. A vaccum line from the intake snorkus runs to one end and out the other another line of equal size runs to the throttle body, just behind the throttle plates. This is opened to maintain a high idle when the car is first started in order to allow the engine to warm up.

Then the idle air control valve (IAC) which should maintain normal idle. Now usually found on the bottom of the throttle body, mine has an adaptor which places it offset so it is easily accessible to adjust and remove. I am going to replace the control magnet with a new one leaving the body of the valve in place(had it off and cleaned it yesterday). Right now thats where I stand

So to be sure we are on the same page with our valve descriptions please respond to see if you are talking about the same thing I am

Tom

Trevor · #9 10-08-2007, 07:46 PM

Tom,

I have always used terminology as per the Subaru manuals in an effort to prevent confusion, unfortunately it appears this has not been successful.

Auxiliary Air Control Valve, (AACV). N.B. this valve is NOT solenoid operated and comprises an electrically initiated coil heater element which heats a bimetal strip, this in turn drives a rotary air valve. It would appear that you term this component as the Cold Air Idle Controller.

Bypass Air Control Solenoid Valve. (BPACSV) or (BPSV). This valve is solenoid operated and control is via the ECU, such that a set idle speed is maintained regardless of accessory engine loading etc. You appear to refer to same as the Idle Air Control Valve, (IAC).

I will continue to use the OEM titles, i.e. as per the Subaru manuals.

In the interim I have been giving further thought to your problem. It occurs to me that you may not have retained all electrical connections as original, which would most certainly upset the apple cart, see below.

(1) The AACV element is energised via a positive supply originating from the fuel pump relay. The heating element in no way responds to control from the ECU. It would therefore appear that the heater/bimetal set up could comprise a form of time delay, so that the valve operates only after an established delay. This would require that the valve be normally open (i.e. when cold), to be closed as a result of engine heat and or electrically after a delay.

Alternatively the AACV may be normally open, and set up such that heat from the engine will close the valve; if this does not occur due to extraneous factors within a set period, to be electrically closed by the heater/bimetal.

As per my previous post, the exact arrangement is for you to sort out.

(2) The BPSV is directly controlled from the ECU and has three electrical connections, one via a shielded wire. This would indicate that the unit incorporates a solid state driver relay requiring a continuous supply, the shielded wire being the low current control signal.

There is no information in the manual showing as to whether control is simply ON/OFF or is modulated. I would expect a simple open/closed device.

You have confirmed that you have checked for possible air leaks etc. and therefore the two items as above must comprise the basis of your problem. I have made suggestions along lines that should enable you to proceed with further investigation.

Over to you, I am keeping my hands clean. Trevor.

TomsSVX · #10 10-08-2007, 08:57 PM

well heres the thing... The BPSV is completely disconnected from the scenario except that it is plugged in, I did this in order to avoid a CEL... As I typed this, maybe it is the ECU being completely baffled as to why the signal is being sent to the BPSV and nothing happening... Hrmmmmm maybe I should hook it back up... Crap, alright Next thing to do is hook that bad boy back up

Tom

Trevor · #11 10-08-2007, 09:06 PM

Quote:

Originally Posted by TomsSVX

well heres the thing... The BPSV is completely disconnected from the scenario except that it is plugged in, I did this in order to avoid a CEL... As I typed this, maybe it is the ECU being completely baffled as to why the signal is being sent to the BPSV and nothing happening... Hrmmmmm maybe I should hook it back up... Crap, alright Next thing to do is hook that bad boy back up

Tom

Disconnected but plugged in?

Not mounted?

Electrically in circuit?

The TCU may not be baffled but the AFR will be upset.

TomsSVX · #12 10-08-2007, 09:44 PM

the vaccum hoses are plugged on the engine and not connected to the cotrol valve. The valve itself is electronically plugged in, in order to avoid a Check Engine Light.

Tom

mbtoloczko · #13 10-08-2007, 10:16 PM

Tom,

I think the cleanest (but perhaps the most difficult solution) would be to modify the ECU code. b3lha has worked out the hardware necessary to download the ROM from the ECU, and he has disassembled some parts of the code. For the last year, I've been involved pretty heavily in the disassembly of the Evo ROM and learned quite a bit in the process about disassembly. From what I've seen that b3lha has done, he definitely knows his stuff. I'd love to have someone like him helping with the Evo ECU.

Everyone ought to pool their money together to give this guy whatever resources he needs to finish the disassembly, and then figure out how to upload a modified ROM to the ECU. Not only would the code be available to fix the infamous idle problems, but all the timing tables, fuel tables, knock correction tables, etc would be available for modification by anyone who has the simple hardware and a PC.

If anyone is interested, here are a few of his pages:

http://www.alcyone.org.uk/ssm/

http://www.alcyone.org.uk/ssm/ecu/index.html

Trevor · #14 10-08-2007, 10:29 PM

Quote:

Originally Posted by TomsSVX

the vaccum hoses are plugged on the engine and not connected to the cotrol valve. The valve itself is electronically plugged in, in order to avoid a Check Engine Light.

Tom

OK Tom.

The valve is not a sensor so that the ECU is not deprived of, or is provided with an incorrect signal, therefore it will not be baffled.

But surely YOU now have your answer.

With both types of valve in hand to push and twiddle while reading what I have set down, (Print it out so you can take it to your workshop) decide on exactly how the system works in practice and you must resolve an answer. At the moment you are groping in the dark.

Stick with it, Trevor *<)

Trevor · #15 10-11-2007, 10:10 PM

Quote:

Originally Posted by mbtoloczko

Tom,
I think the cleanest (but perhaps the most difficult solution) would be to modify the ECU code.

Tom,

I am sure that you will appreciate that in order to explore this option, you must first have the BPSV fully operational. Therefore in any event this will comprise your first option .

Please continue to report on progress, as the results will provide valuable information of general interest.