So here's the deal: My car has developed a fluctuating idle and a sorta stumble at light throttle. The stumble at light throttle has been around for awhile. I thought it was the IACV. I guess it still could be, although I did test the resistance and I did clean it (while still attached to the car, car running). The fluctuating idle developed after I completely sealed the snorkel using GE silicone II. Now, I believe, the fumes from the sealant ruined the front oxygen sensor. I think the O2 sensor was on its way out and the fumes may have pushed it to its limits. No CEL though, and yes the light does work.

 

What do you guys think?

[...]The fluctuating idle developed after I completely sealed the snorkel using GE silicone II. Now, I believe, the fumes from the sealant ruined the front oxygen sensor. I think the O2 sensor was on its way out and the fumes may have pushed it to its limits. No CEL though, and yes the light does work.

 

Silicone can damage an oxygen sensor, but it has to actually reach the sensor. As far as I know, the fumes that are given off during the curing of RTV shouldn't do that (GE Silicone I emits acetic acid fumes, while Silicone II gives off mainly ammonia). The danger is in using RTV that isn't "sensor safe" when sealing parts of the engine that come into contact with crankcase oil or something else containing silicone that can get into the combustion chambers (like if there's a bad HG).

 

I'm assuming that chunks of RTV aren't coming off your intake. But what, exactly, did you seal?

Sometimes maf's are a little picky about the airflow pattern across them. I think they like laminar flow best. Maybe if your snorkel is causing some airflow pattern it doesn't like that might be upsetting the ecu?

For what I actually sealed:

As far as the flow, shouldn't the air filter and the maf screen help level that out. It also occurs when I take the top half of the air box off (with the filter still attached, of course).

Nothing that goes in the intake can damage the O@ sensor. It gets incinerated at 1800 degrees C and 15,000 PSI combustion conditions.

 

If the problem was there before the silicon, and there after, you can rule out the silicon.

 

Have you checked for codes? When was the last tim the car had a tuneup? Did you check for vacum leaks? Si the EGR valve behaving itself?

 

 

nipper

So here's the deal: My car has developed a fluctuating idle and a sorta stumble at light throttle. The stumble at light throttle has been around for awhile. I thought it was the IACV. I guess it still could be, although I did test the resistance and I did clean it (while still attached to the car, car running). The fluctuating idle developed after I completely sealed the snorkel using GE silicone II. Now, I believe, the fumes from the sealant ruined the front oxygen sensor. I think the O2 sensor was on its way out and the fumes may have pushed it to its limits. No CEL though, and yes the light does work.

 

What do you guys think?

 

you should have did it the proper way and bought a new gasket for the IAC.

I never removed the IACV.

 

As far as the intake and fumes see http://www.subaruoutback.org/forums/showthread.php?s=&threadid=8304

 

No codes. The fuel filter, wires, pcv, seafoam has been done in the past 10k. plugs and airfilter in the past 100 miles.

 

The idle problems started after the silicone.

A note: yes, oem wires.

 

1996 2.2 MT = no egr

Ummmm why does it not have an EGR? The purpose of the EGR is to lower temperatures in the combustion chamber so the engine combusts at the right temp. If you removed or someone removed the EGR that could be your problem right there. It will detonate like crazy i would think..or i could be completely out of my element since i dont know as much about the newer gen subys.

Wow I think maybe I need to be more careful spraying silicone all over the place in the engine compartment.

 

I thought egr was more of an emissions device. Yes if the vehicle came with it from the factory then more many states emissions inspection it must be present. I think '95-'96 was a year for lots of changes/differences in this area as odbii was phased in.

as far as the egr....quote taken from http://www.ultimatesubaru.org/forum/showthread.php?t=35906&highlight=egr+valve

 

 

I have a manual trans 96 2.2 L and it does'nt have an EGR valve.

- bottom of first page

 

and I also looked in my engine bay

[...]As far as the intake and fumes see http://www.subaruoutback.org/forums/showthread.php?s=&threadid=8304

 

No codes.[...]

 

The idle problems started after the silicone.

The manner in which silicones can damage an O2 sensor is that high temperatures (even those less than in a combustion chamber) convert them to silicon dioxide. Silicon dioxide is a glass-like insulator, and a very thin film of it on the sensor will prevent it from working correctly. While I've seen evidence that liquids like motor oil can carry away some uncured silicone, I've yet to find a reliable source that indicates fumes during the curing process contain any significant amount of silicone compounds that could be intake-air-borne. (For Silicone II, there's some methanol released, and the moisture cure generates ammonia.)

 

If you believe that your O2 sensor has been contaminated by silicon dioxide, then you might also have reason to be concerned about the catalytic converter; SiO2 can contaminate the catalyst as well. However, since you haven't experienced any trouble codes, that would seem to indicate the problem is still subtle. Are you sure that nothing else was disturbed while you were applying the sealant?

 

The best info I've found so far is from a MSDS (Material Safety Data Sheet) for GE-5000 Silicone II, http://www.e-barnett.com/MSDS/000842.pdf . I'm not a chemist or chemical engineer; if a forum member is, please enlighten us.

I let the silicone cure almost the entire appropriate 48hrs (it was cold out). So, I think that the little bit of fumes that may have reached the O2 sensor threw it out of line just enough to mess with the idle. Since, I believe, the O2 sensor was already on its way out (the slight stumble at light throttle).

 

I ordered a new O2 sensor so I willl know for sure in a few days. No, I am not just throwing parts at my car. I wanted to replace the O2 sensor when I did the reseal but that extra $100 was just too much at that time. So I am doing it now.

Say does your idle still stumble right from a cold start? The o2 sensor doesn't output a useful signal until it's hot enough which takes what maybe a minute or two after startup...

It happens after it's warm.