Not your average P1507

[kevywevy]

OK guys. I've been having a few problems lately with my 97 LGT 2.5 Auto. So it goes like this...

about a year ago i had a P0420 (Catalyst System Efficiency Below Threshold)... replaced the rear O2 sensor and everything was great.
about a month ago i get the p0420 again... no big deal, i replace the front O2 sensor
the P0420 goes away, but i get a P0136 (Rear Oxygen Sensor Circuit Malfunction) instead after driving it a few miles
i figure that can't be right... the confusing thing is that when i replaced the front O2 sensor, there was no way to differentiate between the 2 white wires when i was soldering the universal O2 sensor in. so, i go back and solder the white wires the other way. after about 30 or 40 miles, the P0136 hasn't come back, but I now have a P1507 (Idle Control System Malfunction (Fail Safe)) in its place!

so, its an auto... does the automatic transmission have a neutral switch or something similar that it could be? the idle is fine, so it doesn't seem like it should be anything actually related to the ICS.

any thoughts would be much appreciated.

[nipper]

In subaru speak its called an inhibitor switch. Its on the transmission and tells the TCU what gear you have selected (PRND321).


nipper

[kevywevy]

so, the inhibitor switch could be faulty and throw this code like the neutral switch on the manual trans does?

[nipper]

Yup, especially if you have no running issues.


nipper

[kevywevy]

OK guys, things have changed a little.

So, after a while of driving with the code, in the morning when its been cool out, my engine will die or idle incredibly low when going around a tight corner or braking a little hard. After this happened the first time, I replaced the universal O2 sensor with a new factory one. The P0136 is still there, but the P1507 hasn't come back. Its been about 400-500 miles with the new O2 sensor and P1507 is nowhere to be found.

About half the time, the engine idles high and will sometimes shift weird (down, up, down) when coming to a stop when the engine isn't warm, but its not cold out. When it is "cold" out in the morning (its been pretty nice this summer in the Seattle area) and the engine is cold is when I have the low idle issue.

So, obviously its not the front O2 sensor causing the problem. Could the rear O2 sensor be causing this? Is there much of a difference between the rear O2 sensor the and the front? Could I swap the universal one onto the rear to check... Im pretty sure the connections are different, but is there anything really that different about the sensors?

Thanks for any input guys.

[kevywevy]

Oh, and decreased fuel mileage. I used to get a consistent 25 mixed with 27mpg commuting on the freeway opposite most traffic.
Now, Im usually getting ~22-23mpg.

[Huffer]

i get a P0136 (Rear Oxygen Sensor Circuit Malfunction)

If you're getting a code, and you replaced your front O2, it's now sending a better signal to the ECU that it cannot match with a bad or failing rear O2 sensor. The ECU uses both signals.

[kevywevy]

oh shit. i didn't read slow enough to catch the REAR O2 Sensor Malfunction.

God Im and idiot! HA

So, any idea if I could solder the universal front sensor that I bought at first and use it on the rear to check?

[Huffer]

^^ probably, if it has the same color wires etc.

[ouch1011]

Just FYI, the white wires are for the O2 heater. They are both white because it doesn't matter which way you hook them up as long as one gets switched power, one gets ground. Signal wire is usually grey or blue, sensor ground (if it has 4 wires) is black. 3 wire O2 sensors don't have a separate sensor ground, it just grounds through the exhaust system.

[kevywevy]

thanks for the wire color info.

just for other people's future reference; the front O2 sensor does work in the rear, obviously you have to change the connection plugs and extend the wires for the rear one.

swapping the other O2 sensor into the rear solved my problem of the P0136 code.

BUT, the car would still have idle issues when it was cold outside in the morning, even if the engine was up to normal operating temps. and then after driving about 100 miles with the new O2 sensor in the rear and no CEL, the p1507 came back!!!!!! and the car died a few times and as i was pulling into my driveway after i had restarted it, the engine started having crazy bad idle problems. giving it gas wouldn't really even do much.

also, i don't know if this matters, but whenever it died, i'd throw it into neutral to restart it. once i restart it, the AT transmission fluid light would blink like 5 times, instead of just staying on solid for a few seconds like normal. does this tell me anything, or is it just because i started it in neutral?

man this sucks, i might just take it to a shop :(

off to go search the forum...

[jey]

Try cleaning your idle control valve.

[kevywevy]

ok, i found a pretty good write up on cleaning the IACV. I'll give it a try. Thanks.
http://forums.nasioc.com/forums/showthread.php?t=781242

[kevywevy]

so, obviously the turbo IAC is different than the NA. and the DOHC and different than the SOHC 2.5

can anybody show me a good write up on how to remove the IAC on a SOHC 2.5?! I can't seem to get it off, there are just so many wires and hoses in the way. I think the biggest problem is that i can't get the two smaller hoses off of the IAC itself!

[kevywevy]

oy. finally got it off. apparently there are 4 bolts holding it on :smt011 and mine only had 3 :smt017

so, now my question is do i take the electrical sensor off the top to clean inside?

http://img257.imageshack.us/img257/3929/iacxz7.th.jpg

so is it ok to unscrew the two top screws? or is it easiest to just spray carb or brake cleaner in there rather than taking it apart and using rubbing alcohol and qtips?

[kevywevy]

anybody?

[jey]

I would mark the position of the screws (since I think it's adjustable not fixed) and remove the 2 screws from the top. Then you can clean it out and check the movement/clean the valve itself as well as the stepper motor that turns it.

[kevywevy]

well, taking the top electric part off doesn't help much. all it did was allow me to spin the mechanism inside. i had it soaking in rubbing alcohol for a day or two and there was lots of gunk in there. so with some qtips, engine bright and a few more dunks in the rubbing alcohol, its looking pretty clean inside from what i can tell. now i just need a new hose from subaru, since i broke one. i'll do that tomorrow since i have to go to work pretty soon.

thanks for the help. im keepin my fingers crossed.

[kevywevy]

ok. i just really suck.

cleaned the IAC and put on a new PCV valve. the idle problem seems to still be there, but we'll see for sure or how bad in the morning when its cold out.

but now my temperature gauge isn't working. are there any sensors that i might have unplugged and forgotten to plug back in somewhere around the IAC? i double checked and didn't see any that i unplugged when i took the IAC out.

but i did find this wire, which i can't find where its supposed to connect to. maybe it got unplugged while i was taking it out. any ideas of where it goes/what it does?

http://students.washington.edu/kevinl3/Legacy/IAC.JPG

[jey]

Check the coolant temp sensor, which sits on the coolant pipe between the block and the intake manifold on the passenger side.