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Old 03-23-2005, 11:26 AM   #1
Scooby Newbie
Member#: 82547
Join Date: Mar 2005
Chapter/Region: MWSOC
Location: Kalamazoo, MI
2010 Forester

Default IAC - 6-wire vs. 3-wire - P1507 CEL

I have a 97 Impreza w/2.2l - EJ22. The ECU repeatedly logs a P1507 (IAC fail-safe) fault. The idle consistently drops way low when warm, and the ECU goes into safe mode.

I've been trying to determine how to test my IAC and also how to test the signal being produced by the ECU. The best I can tell is that on my three-wire IAC, it's pins 13 (to open) and 14 (to close) on the ECU that control the IAC. The voltages on these two pins should vary from 1-13, according to the documents I've seen. However, most wiring diagrams that I've seen show a 6-wire IAC on the '97 EJ22, but a 3-wire on the '98.

I have a few questions for the gurus out there:

1) Might I have a late model-year '97 that is using a '98 wiring setup? What should be the Ohm reading between the three pins on the IAC solenoid.

2) Should my three-wire IAC valve itself be spring-loaded to return to a 'default' position when no power is being delivered to the IAC.

3) It is possible to eliminate this PITA all together? The dealer wants $300+ for a new IAC <ripoff>.

4) It is possible to setup a 'customized' IAC that is intended for a different motor altogether (e.g. a GM, Chrysler, or Ford)?

5) Could a dying (fluctuating watts and voltage) alternator be delivering too little power to the solenoid causing it to behave poorly and log the P1507?

Question to self: Do I buy a $150 alternator first, or a $331 IAC - drats!!

Thanks in advance,

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Old 03-23-2005, 10:59 PM   #2
Scooby Specialist
Member#: 49087
Join Date: Nov 2003
Chapter/Region: RMIC
Location: Inside your carnot cycle
1998 RST V8 STi swap
'05 R6 '95 BMW V8 hotness


Why do you suspect an alternator?

If you have an automotive stethescope (or something like a long screwdriver) you should be able to hear the IAC cycling at idle. It is just a solenoid that is cycling on/off really fast. You will hear a buzzing type sound from it. It sounds like you have some freaky mid production car that got the '98 idle control. As long as you are seeing a reading typical with a solenoid coil (a few ohms) and no opens on the solenoid it should be electrically good. I've never seen an actual schematic for a suby solenoid IAC so that's just a guess.
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Old 03-24-2005, 09:52 AM   #3
Scooby Newbie
Member#: 82547
Join Date: Mar 2005
Chapter/Region: MWSOC
Location: Kalamazoo, MI
2010 Forester

Default why alternator?

Why do I expect a bad alternator?

I have a strange pulsing, flickering, and dimming of all electrical while simply idling. My windows are all s-l-o-w, my heater blower seems sluggish. My headlights are generally less bright that I would expect them to be.

If my overall voltage is a bit low, 10-12v, could that affect the IAC solenoid's ability to hold the valve in the proper position? Low voltage seems like it could be the underlying cause of the whole problem...but I'm just not sure.

I'm thinking that I should start with replacing the alternator, then move on to replacing the IAC if the problem still persists; moving from the least to the most expensive parts.

Thanks a ton for the reply and the input...I'm really suffering on idle - going in to safe mode at least twice in a 5 mile drive in city traffic. <bummer>

I can't get the alternator till next week says my wallet , so I'm suff'rin til at least then.

Is my alternator internally regulated? What voltage should my alternator output be? ~12-14? I should see a steady voltage reading - It shouldn't waver more than a volt or two, right?

Sorry such a suby n00b with so many ?????s I sure hope to be able to offer help back to the forum members once I get smart here.

Thanks again!

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Old 01-10-2009, 09:44 AM   #4
Scooby Newbie
Member#: 199736
Join Date: Jan 2009
1999 Impreza 2.2,CAI

Default Alternater?

Hey, I know this thread is really old but I'm wondering if anyone else has had alternater problems do this to their EJ22? I have a 99 Impreza and it's basically doing the same thing. Except the idle goes all over and if you are in gear and you let the rpms go below 2000 the car sometimes acts like its posessed... i.e. it will suddenly lurch forward without you pressing on the gas, or opposite, suddenly slow down.

The ECU also goes into safe mode (I guess? --CEL, p1507) and the car idles around 750-800 rpms but runs pretty badly. Plus, the car starts really roughly when it's cold in the morning during winter months.

Anyway, I read some stuff about neutral switches in another thread so I replaced the neutral switch and it made a huge difference. It didn't fix it though! It just made the car run REALLY smoothly. The idle still fluctuated alot. AND it still started horribly in the morning.

So, the next day I disconnect the battery, remove throttle body and clean thoroughly, including removing and cleaning IACV. Put it back on the car and replaced the TB gasket. Start car and WOAH idle at 2500 rpms. Tried adjusting TPS but as idle approaches 1k it suddenly drops to 4-500 rpms. I try to turn back up and it suddenly jumps to 1500.

I have IACV on the way from a subaru dealer. Will post back when I replace it.
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