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Old 03-12-2012, 12:38 AM   #51
Scooby Newbie
Member#: 107205
Join Date: Feb 2006
2007 Impreza 2.5i


I'm having issues with this code as well, however, my wife's Subie is an automatic 1997 Outback. We bought it not running worth a crap, they thought it had a blown headgasket, but it was just the timing belt. Reinstalled the belt, pulleys, and tensioner, checked compression.

Now, when I turn it on, it will run at about 2000rpm for a minute or two, then drop down to about 1000rpm, pop a CEL code, and then runs like crap. Sometimes the engine shakes, like it's running on 2 or 3 cylinders, other times just runs really rough. I've replaced plugs, wires, and checked the coil pack. I've tried starting it just with 1 and 2 or just 3 and 4, and will run soso with either set of cylinders.

I'm baffled. I'm going to take apart the intake assembly and see if anything is gunky and/or not running ok and will post back. The only thing I can think of is the IAC.
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Old 03-12-2012, 05:48 PM   #52
Scooby Newbie
Member#: 124694
Join Date: Sep 2006

I've sold my car over a year ago, but still get notifications on this thread being active... so just to restate what my final experience was:

I had no problems after a thorough cleaning of the IAC valve. be sure to look inside every rubber hose you remove in the process of getting the IAC off the car. The thick rubber hose that came in from the side was quite big, yet it was completely shut with packed in dirt. I'm talking dirt packed so tight, you have to push it out with a screwdriver and then spray down the hose and clean out the remainder. The entry to the manifold was also completely blocked off and packed with dirt. A good cleaning was all it took to restore the idle back to normal and prevent the engine from going into limp mode.
Hope this helps someone out.
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Old 01-28-2013, 10:22 AM   #53
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Member#: 194453
Join Date: Nov 2008
Location: central NH
2001 Legacy 2.5 GT
Winestone Pearl


Sorry to bring back an old thread but my 98 ob does the same thing. P1507 IACV fail safe, 1540 speed sensor. I did a 4eat to 5MT swap using a completely different engine. IT DID NOT SOLVE ANYTHING! So far the only thing left is speed sensor (used from previous 4eat). Just replaced that and it still does the same thing. MAF, replaced, still does the same thing. It's not the neutral switch or ANYTHING on the engine. The only thing that I havent replaced is the cat/AF/o2 sensor, and the engine computer. Idk if there's a bad connection somewhere or what..... But I'm pretty stumped.
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Old 01-31-2013, 09:39 AM   #54
Scooby Specialist
Member#: 111565
Join Date: Apr 2006
Chapter/Region: W. Canada
Location: Winnipeg
1999 Legacy 2.5GT
2007 Legacy GT Spec-B


I was dealing with that P1507 code for months. I tried changing the neutral position switch and within 1 km the light was back on and my car was stalling randomly again.

Last thursday I decided to pull the IACV off(wow was it dirty!!) and gave it a proper cleaning and it has been working ever since. I sealed up the back end with duct tape, filled the unit with seafoam and then let it sit for a few hours. I then drained all the fluid out, cleaned all visible parts with q-tips and blew compressed air into the unit. Since then it's been idling perfectly, no stalling and no more check engine light.

Caschmidt, try cleaning your valve and see if that is indeed your problem, it takes less then an hour to do and the gasket only costs a few dollars.
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Old 02-05-2013, 02:41 PM   #55
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Member#: 8124
Join Date: Jul 2001
Location: Denver, Colorado
1998 Old Grey Mule
Regacy Rype R


I had this problem for the first time yesterday. High idle, CEL, stuttering, limp mode 5mph home.

So far I wirebrushed the battery terminals and cleaned my K&N filter. Cleaning the terminals (which were very corroded and dirty) reset the ECU.

So far so good. The problem hasn't reappeared.
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Old 05-09-2013, 11:38 AM   #56
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Member#: 355948
Join Date: May 2013
1998 Subaru Forester


I'm having the same problem with the 1507. I also have a misfire on cylinder 1,2,4, an 0440, 0500 and 1540 code... Any thoughts?
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Old 05-10-2013, 02:52 PM   #57
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Member#: 336666
Join Date: Oct 2012
Location: CANADA
1997 impreza wagon


i think i may be having the same issue as all of you, I've got a 97 impreza 5spd brighton wagon 1.8Lame, with 180xxxkm when i first got the car it ran rough and had a high idle (winter), had exhaust leaks etc etc i was getting p0141 (o2 sensor) and the code where idle is higher than expected (p0507?)
i cleaned the entire intake from the MAF to the TB, got a new exhaust and idle was a little more tame, (still cold weather)
then was getting horrid gas milage (7mpg) so i changed the WAY out of spec plugs, which fixed that.

-now that its warming up my car will start to limp once and a while on hot days (like described above)

-its weird tho, i went on a 80km trip with no issues and great driving (chilly spring day)

-then today (20 and sunny), stop and go traffic, taking small trips etc, on my way home it started limping right before i got home, could barely even hear my engine running while at a stoplight, so i plugged in my obd dongle and logged all codes for the next 3km i got home and screencapped the codes i got along the way and shut off my car, letting it sit for 5sec i turned it back on, and it was normal again.
i got these codes
p0141 (O2 sensor)
P0264 (Cylinder 2 Injector Circuit Low) <---- would explain the limping/shaking engine?
P0507 (Idle Air Control System RPM Higher Than Expected)
P1507 (Idle Control System Fault (Fail Safe Mode)

im going to try the neutral switch, aswell as checking the voltage on my injectors, dont feel like spending $200 on a iacv for a 1.8L would rather buy a whole new engine haha

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Old 05-27-2013, 11:12 AM   #58
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Member#: 341058
Join Date: Dec 2012

Originally Posted by jkastrin View Post
I'm having the same problem with the 1507. I also have a misfire on cylinder 1,2,4, an 0440, 0500 and 1540 code... Any thoughts?
The P0440 is an EVAP malfunction code. The P1507 is manufacturer specific which you wouldn't be able to figure out without taking it to Subaru and the P0500 is for vehicle speed sensor malfunction. The misfire could either be due to a vacuum leak, faulty injector, ability spark plugs, spark plug wires or ignition coil pack.
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Old 09-18-2013, 01:37 PM   #59
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Member#: 328933
Join Date: Aug 2012

ive got this problem going on with my girl;s 99 legacy. its an auto. ive already replaced the iac which helped slightly and fixed the p0505 or whatever for the iac but the 1507 is still there. would the NSS or inhibitor switch on the tranny be the cause too? from what ive been reading it mostly fixes it on the manuals and I cant find anything about it fixing it on the autos
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Old 04-25-2014, 08:02 PM   #60
Scooby Guru
Member#: 13910
Join Date: Jan 2002
Chapter/Region: NESIC
Location: Greenwich, CT
1997 Legacy outback


got these codes p0507 and p1507 on a '99 Legacy SUS

I cleaned the IAC with carb cleaner so where it moves freely very very easy.. plenty of slack on the throttle cables..

SO the only thing I did not do now is change the PCV valve..

it's a very annoying code.
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Old 10-03-2015, 04:09 PM   #61
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Member#: 170856
Join Date: Feb 2008
Chapter/Region: NWIC
Location: Portland, OR
1991 SS "the Clone"


I've read this thread with great interest. 1998 2.5 OBW Outback Wagon. Automatic transmission. I had a p1507 so I cleaned the IAC by blasting brake cleaner down the rubber inlet while holding the rpm at 2000. Let idle 10 minutes This is Subaru's recommended cleaning procedure.
Code came right back. I replaced the IAC with a known good used one, got code p0507, no worries. Reset the IAC duty ratio to 32.5% using a Subaru select Monitor and all is good. I haven't seen any posts yet that talk about resetting the duty cycle to 25-40% after replacing the IAC. This is an important last step after messing with the IAC. Basically you're loosening the two small screws on top of the IAC and rotating it. In my case it was rotated clockwise about 1/8 inch. The idle slowly adjusted, 3-4 second delay, and all was well. Long test drive, several restarts so far. Behavior is night v. day. All fixed.
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