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I have a 2002 Impreza 2.5RS engine in my VW Vanagon that has had erratic idle for a couple of months now.

 

The engine seems to run OK when first started, (cold) until it goes closed loop. Then it idles fine for about three seconds, then stumbles, and struggles for the next three seconds. This cycle repeats indefinitely, over and over.

 

It seems to run fine when the throttle is advanced to higher rpms.

 

I'm wondering what sensors might cause this repetitive cycle that I could try replacing.

 

Oxygen Sensor ?

IAC valve ?

Throttle position switch ?

 

I have another engine with most of these that I could try switching some of them out.

 

Any thoughts or tips appreciated.

 

W

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possibly the o2 because in those years they had that goofy o2 sensor with the air flow meter. we just had the same issue last week in an 02 forester.

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possibly the o2 because in those years they had that goofy o2 sensor with the air flow meter. we just had the same issue last week in an 02 forester.

 

Yes, this engine has an AFM. Can you tell me more about the O2 sensor.

 

What's "googy" about it? Only extra O2 sensors I have around are from 90-94 Legacy's and a new one from the dealer is expensive to buy.

 

Warren

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Yes, this engine has an AFM. Can you tell me more about the O2 sensor.

 

What's "googy" about it? Only extra O2 sensors I have around are from 90-94 Legacy's and a new one from the dealer is expensive to buy.

 

Warren

 

The o2 sensors from the aftermarket may not be as relaible or reactive as OE.

If you have two sensors, the first should be OE, the 2nd can be anyones. The first talks directly to the computer and controlls emissions, the 2nd just measures that cat's output.

 

nipper

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Nipper do you think that it would be safe to say that more than likely the front O2 sensor can be replaced without worrying about the rear one since most idling problems are related to it's function?

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Nipper do you think that it would be safe to say that more than likely the front O2 sensor can be replaced without worrying about the rear one since most idling problems are related to it's function?

 

Yes. The front o2 snesor seems to wear out quicker then the 2nd, since the first is exposed to unprocessed fumes.

 

nipper

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Nipper do you think that it would be safe to say that more than likely the front O2 sensor can be replaced without worrying about the rear one since most idling problems are related to it's function?

 

A friend of mine who prepares the SOHC 2.5L for use in airplanes and gyrocopters tells me they don't use the second sensor at all since it has no effect on how the engine runs....it only tests the condition of the second CAT to tell if it's functioning or not. Experimental aircraft with Subaru engines don't use any CATs.

 

I don't currently have the rear 02 sensor hooked up either, since the wire to it fell down onto my muffler and the connector was melted. But the idle symptoms I have now were occuring before that happened....and after...no change. I don't consider it part of the problem, although I get a code for the missing sensor.

 

Warren C.

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i mean it is goofy just by its design in comparison to other designs.

 

I sometimes hear the term "wide band 02 sensor" ?

 

Is that what this engine has?

 

What's different about 'wide band" vs any other sensor.

 

W.C.

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Try putting a 2.2K ohm resistor in the plug for the 2nd o2. you can buy 5 of them at Radio shack for under a buck or two. Just bend the prongs in and stick it into the terminals.

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I can give you one good data point for aftermarket O2 sensors. I have bosch generics in both the front and rear spots on my 96 OBW, and they have been working fine for 9+ months now. Given the physics/chemistry of how they work, these aftermarket jobbies might wear out faster, but they'll provide exactly the same voltage variation while there's still enough reactant left in the probe for them to work... so cheaper is OK, if you are willing to trade lower cost for the possibility that you might have to change them out sooner. Again, the Bosch generics work just fine in both positions, at least for my 2.5L exhaust. Passed Colorado state emissions inspectin with flying colors, too -- better numbers than I had on the last test I had done, in California a couple of years back....

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they arent gonna work for his style of sensor. of yours is the one i am thinking of it has that flip lever clamp that holds the connector together, it is a completely diff animal than any other you have seen. i dont know alot else about it except is seems to be the new expensive subaru issue that can cause a ton of drivabiltiy problems without throwing a light. we have done a couple so far at work, one last week on a forester and another on an RS that i swapped.

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it is a completely diff animal than any other you have seen. .

 

 

So tell me, What kind of "diff animal" is it?

 

That's what I'm trying to find out.

 

"Wide Band" ??? "Narrow Band"?? Something limited that only works with the cars that have an AFM??

 

Please enlighten me..

 

Warren C.

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i am not completely sure, like i said it is a diff plug setup. from what my boss tells me (so dont quote me on this) if you notice the car has no mass air, he said that sensor also determines airflow along with normal frunctions of oxygen measurements and heating.

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