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Hi guys, was wondering if anyone could throw in their 2 cents concerning my sti's problem that just started. A few weeks ago I noticed the car (22k on it now) started running alittle rough at low rpm's. The tach would drift up above the 5-600 rpm and then dip down to 2-300, then back up. I didn't think much of it because the weather here has been hot and humid but it started happening more frequently and I even noticed that the car started to almost sputter to zero before righting itself and jumping back up to 5-600.
Then about a week ago it actually stalled on me a few times as I put the clutch in and slowed to stoplights. I would feel myself lose power steering and that was my hint that the dash was lit up and the engine at zero. I thought maybe I had a bad tank of gas but then when I got another tank the other day the problem didn't go away. So on Monday I put in a can of BG44K thinking that maybe my injectors had some carbon build up on them. I decided to drive the car really hard over the past two days hoping to clear out any carbon that might be built up from my 7 mile trip to work each day. Well, the problem has still been occurring. The car has actually stalled on me probably 6-7 times over the past week. I was at Subaru Wednesday dealing with my wife's car and mentioned it to one of the techs. He hooked up the scanner and reset my ecu and said to drive it hard. I've been driving it hard since then but it stalled again on me approaching a light this afternoon. I pulled out the air filter and it looks fine. I also notice that it doesn't necessarily depend on if I have the a/c on, fresh air on, or all off.....it seems to happen frequently in all three cases. I just drove home from work a few minutes ago and it was running fine but i'm sure i'll see this behavior again in the morning.
Thoughts?
 

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Discussion Starter #3
nope.....the only mod is an sti air filter (which is basically just a replacement to the stock on), uses the stock box so I hardly call it a mod at all.
 

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Mine did the same thing. Then it developed a miss in cylinder #1. I am in the process of replacing the plugs...don't know if this will fix the problem though. All 4 plugs were fouled a little.
 

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silversti said:
Mine did the same thing. Then it developed a miss in cylinder #1. I am in the process of replacing the plugs...don't know if this will fix the problem though. All 4 plugs were fouled a little.
How many miles did you have on the car when it first happened?
 

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I had about 7k on mine when I went on a cross country road trip. After a couple of hours of cruise control the engine will tend to die at idle after restarting it. This is the hot-start issue that is common with turbo charged cars.

When this occurs with your car is it after a length of driving or hard driving?
 

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It may be, it may be the MAF being overheated, who knows. I know I had a '91 talon TSi that did the same thing when it was really hot. I came to know it as just part of the game.
 

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I had the same problem with my 04 wrx and Subaru had to replace the idle control valve and the rear o2 sensor...so that might b the problem....if you want you can try and clean your MAF with non-chlorinated brake cleaner....do a search about it and youll get some info on it
 

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Discussion Starter #10
when?

Vexamus said:
I had about 7k on mine when I went on a cross country road trip. After a couple of hours of cruise control the engine will tend to die at idle after restarting it. This is the hot-start issue that is common with turbo charged cars.

When this occurs with your car is it after a length of driving or hard driving?
It depends, a few times it has stalled after being driven for awhile (not necessarily hard or long mileage) while other times it has stalled shortly after leaving the house. Last night it drove fine home and this morning on the way into the office it was idling fine. I am down to less than 1/4 tank of the BG44, if it still stalls after the next fill up i'm taking it in.


I called my old dealer in CT and he was going to do a search in his subaru dealer/engineering database to see if he could locate anything on it. I have not had a CEL at all during any of this.
 

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Discussion Starter #11
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Well, i've run through one can of BG44K and just filled back up. I actually had it in the shop yesterday but of course the problem could not be replicated. The guy was nice enough to give me a few cans of their fuel injector cleaner. I threw another can in last night but now i'm not so sure its the fuel system. It has not been as bad the past few days but it did stall on me once last night. I'm starting to think it has to do with the idle control or either the belts because I kicked on the a/c yesterday and when I was slowing down to a light I put the clutch in to disengage and I noticed that the tach goes down from say 2200 to almost 0 in the first few sec's then rights itself to 500. Now in the case last night, it would go down but actually hit zero and the engine was stalled. What is perplexing is that it does not happen everytime I'm driving the car. Sometimes I will sit at a light and the car idles perfectly on the hashmark (500 or whatever that is), whereas other times it won't. Most of the stalls have occured when decelerating to stop. Could it somehow be related to belts as it does seem to occur more with the a/c on then off. You would think the opposite because generally when you kick the a/c on the car idles an extra 1-200 rpm higher.
I still have had zero CEL's so the dealer doesn't seem to be concerned. The power seems smooth when driving around either gently or hard so its not happening during acceleration. It's just annoying as hell to look down and see the car completely stalled out with no explanation.
 

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one thing that may be bad is the fuel filters...if u got some nasty crap in them it is possible that u will get a rough idle or yor car will stall...if u r not sure where they r located, they are the black circles about the size of a silver dollar just to the right of the i/c..if u go to auto zone, u can buy some really nice in-line fuel filters that are glass encased....they look really nice and actually allow more fuel through....if u do this though, i would suggest buying the next size up fuel lines, the stock ones are really small and are a pain in the a$$ to take off and even worse to put back on...u will also need bigger line clamps as well...it shold only cost $25 for everything u need....
 

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Discussion Starter #13
I'm getting some feedback that it might be a vacuum leak somewhere in my system.......going to check that out tonight when I get home
 

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After reading your symptons, and the inconsistancy associated with your RPMs stalling (they aren't predictable at all), I am almost willing to bet that it's your 02 sensor. If it was vacuum, it should be fairly constant, or in some way predicatable. With an 02 sensor, usually it's caused by a coating over the sensor that makes the response very slow, resulting in a lean or rich condition. This can lead to detonation, poor gas mileage, hesitation on accelaration, stalling, surging, rough idle, and really screws up your emissions. A simple oscilliscope check by the dealer would verify if it is working correctly.

I tend to stay away from any fuel additives just for this reason. You never know when that fuel injector cleaner (crap IMHO) or octance booster is going to loosen some carbon and deposite on your 02 tip, or even worse, morph into a compond that really likes to stick to things. Some additives are highly hydroscopic, which means they absorb water very easy, and your 02 sensor hates water!! Another good failure cause is for those over enthusatic builders who like to slather on the silicone when re-gasketing a head or something. A big no no, as this will assuradely coat your 02 sensor.

They aren't that expensive. I'd just get it replaced for consciance sake and see what happens. You can drive yourself crazy trying to find an "intermitent" vaccum leak, let alone even verifying that it is the cause.

Please let us know how it turns out and good luck.
 

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Discussion Starter #15
YBNormal07 said:
After reading your symptons, and the inconsistancy associated with your RPMs stalling (they aren't predictable at all), I am almost willing to bet that it's your 02 sensor. If it was vacuum, it should be fairly constant, or in some way predicatable. With an 02 sensor, usually it's caused by a coating over the sensor that makes the response very slow, resulting in a lean or rich condition. This can lead to detonation, poor gas mileage, hesitation on accelaration, stalling, surging, rough idle, and really screws up your emissions. A simple oscilliscope check by the dealer would verify if it is working correctly.

I tend to stay away from any fuel additives just for this reason. You never know when that fuel injector cleaner (crap IMHO) or octance booster is going to loosen some carbon and deposite on your 02 tip, or even worse, morph into a compond that really likes to stick to things. Some additives are highly hydroscopic, which means they absorb water very easy, and your 02 sensor hates water!! Another good failure cause is for those over enthusatic builders who like to slather on the silicone when re-gasketing a head or something. A big no no, as this will assuradely coat your 02 sensor.

They aren't that expensive. I'd just get it replaced for consciance sake and see what happens. You can drive yourself crazy trying to find an "intermitent" vaccum leak, let alone even verifying that it is the cause.

Please let us know how it turns out and good luck.
Thanks for the feedback, I will definitely look into replacing that but one question, wouldn't I be getting a CEL for the O2 sensor, especially if the car was detonating?
 

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Not necessarily. If the 02 sensor is still functioning, but just providing slow response, the ECU could determine this as being acceptable. As far as detonation goes, the majority of det occurs well below our hearing threshold, which is why our cars come equiped with a knock sensor. Unfortunately, either due to the type or location of the sensor, or because of the inherent noise of our blocks, our knock sensors tend to "wash out" at higher RPM, causing the ECU to pull timing and/or increase fuel flow (has to do with stoichiometrics...more fuel cools the combustion chamber, slowing the detonating fuel flash down, and reducing the "explosion" force"). Note that if this is actually happening, you can get fuel wash into the oil and excessive unburnt fuel into your exhaust, further compounding the 02 sensors ability to respond.

What this means in real life though is that your car could be detonating without you being able to actually hear it.

One thing I also thought of was the type of gas you run. Hopefully it is at least 93 Octone (or 97 RON from EU standards).

Since you have already involved the dealer, ask them to swap out the 02 sensor just to see if the problem goes away. A data logger would also help in determining the problem, or at least helping you to demonstrate to the dealer there is a problem.

Since you are considering replacing the 02 sensor, you might want to look into a wide-band system. Much wider and faster response....greater sensitivity, etc. But you pay for it. If you have intentions on doing any mods later, this is a definite step to take.

Good luck.
 

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Discussion Starter #17
YBNormal07 said:

One thing I also thought of was the type of gas you run. Hopefully it is at least 93 Octone (or 97 RON from EU standards).

Since you have already involved the dealer, ask them to swap out the 02 sensor just to see if the problem goes away. A data logger would also help in determining the problem, or at least helping you to demonstrate to the dealer there is a problem.

Since you are considering replacing the 02 sensor, you might want to look into a wide-band system. Much wider and faster response....greater sensitivity, etc. But you pay for it. If you have intentions on doing any mods later, this is a definite step to take.

Good luck.
I always run 93 in it and with this problem i've been doing "different" stations/brands just to weed out the idea that it was a bad tank of gas....I've gotten a tank of Shell, Mobil, Exxon, and it doesn't seem to matter. In terms of the 02 sensor, what type of cost do you envision (both going stock or going with wide band)? I'm getting to the point where I'm so sick of this i'm about to say "do the entire 30K service at 22K miles, plus fuel filter, 02 sensor, and replace all drive belts"........yes, a complete waste of money but i'm hoping that somewhere in all that it will get rid of the problem.
 

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I believe we have 2 sensors, one upstream and one downstream of the cat. They range in price from about $60 to $220, depending on the number of leads and the manufacturer. Bosch is probably the best, and it might even be who supplies our OEM sensors.

After some more thought, a wide band probably isn't for you, as without an aftermarket logger/ECU controller, it won't do anything for you as it isn't likely to be compatable with our stock ECU.

The swap isn't that complicated, so rather than pay for an entire service call, just ask them to swap them out and if the problem goes away, they should pick it up under warranty. If not, then you pay. Also, don't forget the earlier posting where someone mentioned the fuel filter. This could also be your culprit. And I know this may sound silly, but have you checked you intake are filter housing and line to be sure it isn't full of crap or maybe something is stuck up in it? You just never know.

Wish I could be of more help.
Scott
 

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Discussion Starter #19
YBNormal07 said:
I believe we have 2 sensors, one upstream and one downstream of the cat. They range in price from about $60 to $220, depending on the number of leads and the manufacturer. Bosch is probably the best, and it might even be who supplies our OEM sensors.

After some more thought, a wide band probably isn't for you, as without an aftermarket logger/ECU controller, it won't do anything for you as it isn't likely to be compatable with our stock ECU.

The swap isn't that complicated, so rather than pay for an entire service call, just ask them to swap them out and if the problem goes away, they should pick it up under warranty. If not, then you pay. Also, don't forget the earlier posting where someone mentioned the fuel filter. This could also be your culprit. And I know this may sound silly, but have you checked you intake are filter housing and line to be sure it isn't full of crap or maybe something is stuck up in it? You just never know.

Wish I could be of more help.
Scott
I had several people also comment on nasioc saying that they were pretty confident that it was a vacuum leak somewhere, do you think that could be it as well? Gonna see if I can take it in tomorrow or Wed with the goal to swap out he 02, fuel filter, and check all the hoses/intake system. Was just out driving it a few ago with the a/c off and it almost stalled......this is so damn annoying.
 

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Yes, it could be a vacuum leak. A vacuum leak could cause all of the issues you spoke of, so don't count it out. A leak down test will determine if you have a vacuum issue, and the dealer can do this easily. Finding it is another story though.

Since all of your issues are at low RMP, it is obviously a flow issue...either air, fuel, or vacuum (which is actually a pressure issue, but it all relates to flow). Focusing on the items you listed should find the cause. Good luck!
 
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