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I have a good felling that my oxygen sensor is failing. I can move it in and out of the exhaust about a cm without loosening it. I have located one that is at the start of the exhaust, right after the turbo, but I am not sure if there is another one. Anyone know? I can't find an answer on the interest as most of it is on newer models. Thanks!

There should be another further down the exhaust just after the Cat I believe.

On the 93-96 WRXs you should only have one on the dump pipe. The one after the cat is a thermocouple that causes a light on your dash cluster if your cat fails.

Ah okay, thanks. My car is having some VERY bad idle issues. The idle is fluctuating all the time at about 1,500k rpm. The O2 sensor is in pretty bad shape so I am guessing that it causing it.

I don't know if your car is AT or MT and whether it is different from N/A to Turbo, but on my 03 XS Forester 5MT that symptom was caused by a faulty Neutral Switch.
Now don't ask me to find where the part is located on the car as it was fixed by my Service Workshop.

Just putting up my fix as it may possibly be the same for your car.

I have found a "neutral position switch" in the car manual, connected to the "ECM" however this is not one of the fault codes. My car shows me 2 CEL codes and my mechanic used his very expensive fault code reader to pull out 7. The oxygen sensor is one of them. I pulled it out and took a photo. It looks pretty bad. I can't find a part number on it though, the only thing I could find was "48k". The screw part is very loose and I can move it very easily which may be the reason why I can smell A LOT of fuel/exhaust fumes in the engine bay when the engine is on. I think the exhaust is leaking out of this sensor.
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That doesn't look like an O2 sensor more like the thermocouple RSR555 was talking about.

an O2 sensor should look like this




Was that in the dump pipe?

TOONGA

Yeah, it was in the large pipe, leading under the car, right after the turbo. After looking at pictures of thermocouples, it looks much more like them than an oxygen sensor. This sensor has a 2-pin connector, if that helps. Is it possible this sensor is in the wrong place?

It could well be. I can't find any accurate information on the exhaust system for the 1993 WRX as all of the FSMs I find are aftermarket pieced together from other FSMs.

From what I understand the O2 sensor is there and the thermocouple is at the back of the cat.

You will have to wait for someone who has?had? this model to tell you for sure.

That sensor looks stuffed by the way

TOONGA

From this diagram here: http://www.ellisfamilyalbum.com/Car%20S ... iagram.jpg it seems that the sensor is meant to be in the up-pipe. I don't know which model WRX this diagram is of though.

Best way to find out is to look at your engine exhaust manifold. if it is the type with the thermocouple in the dump pipe your first O2 sensor will be in the engine exhaust manifold, as in the picture below (on the left of the picture)



stolen from nasioc

then you may have one just before the catalytic converter.

TOONGA

Okay I think I found it. This one has a 3-pin connector. I wont be able to find the one near the catalytic converter until I jack the car up.
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Ok so the thermocouple is where it should be but stuffed or if you are lucky just in need of a good clean.

The O2 sensor looks to be the original from 1993, which means while it may still be sending the ECU a signal it woudn't be very accurate.

You may or may not have a second O2 sensor.

TOONGA

Would you know what kind of spray I can use to clean the thermocouple? Also, is the screw part of the thermocouple meant to be that loose?

The thermocouple should not be loose there should be no movement at all when the flange nut is tightened up. if there is still movement when the nut is tight then the fitting has failed.

As for cleaning it a soft brass brush should clean the scale off it.

TOONGA

Tomi wrote:Ah okay, thanks. My car is having some VERY bad idle issues. The idle is fluctuating all the time at about 1,500k rpm. The O2 sensor is in pretty bad shape so I am guessing that it causing it.

Tomi wrote:From this diagram here: http://www.ellisfamilyalbum.com/Car%20S ... iagram.jpg it seems that the sensor is meant to be in the up-pipe. I don't know which model WRX this diagram is of though.

Looking at that first picture, I'm thinking that this is a thermocouple for an aftermarket exhaust temp gauge. The factory one has only one wire and is at the bottom of the cat in the dump pipe (just before the bend that goes under the car). If your O2 sensor is in the crossover to up pipe, then your engine is an early WRX import engine. In the Au delivered WRX the O2 sensor (3 wire model) is just after the turbo in the dump pipe where it bends down to the cat. The diagram picture you have is of a later model.

If your engine is changing RPM at idle, then I'd be looking at air intake, not exhaust air. Is the engine throwing any codes?

Yeah the engine throws a bunch of codes. The only one I can get from the car myself is code 24, for the IACV, this is most likely the cause because the CEL would come on regularly. The mechanic I go to used his fault code reader and pulled out these ones:
Parking position switch (I heard this is only for automatics so no idea why it is showing up)
Turbocharging pressure control output signal
Accelerator pedal switch
Vehicle speed sensor
Oxygen sensor
Idle control system malfunction
Fuel injector #2

He also wrote down the fault code history, which the car used to have before the service:
Throttle position sensor circuit
Fuel injector #1, #3 and #4
Crankshaft position sensor

I am assuming the oxygen sensor and the IACV are the main trouble causes. I have had small problems with the idle for a long time especially on cold starts however it has just become a whole lot worse.

With that many codes of all different systems, I'd be looking to change your Ignition Relay before starting to change other parts.

Even a manual car has a neutral switch. It's there so the ECU can protect the engine from over revving whilst in neutral but I doubt you'll have an issue with the switch unless someone have been playing around with your wiring.

I think it would be best to have your system cleared via Subaru select monitor, then start from there.

Well the biggest problem with my car has finally been fixed! I have finally got around to properly cleaning the IACV. I left it in a container of petrol for a few hours, then used ear buds to start scraping off the dirt and grime inside. The previous method of using carby cleaner didn't do anything. The car now idles perfectly with no CEL as of yet. Lucky all it needed was a good clean as a new IACV costs $980 retail as I found out from Frog.