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Old 05-25-2013, 03:08 AM   #1
SwedeSTi
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Default NEED HELP - 2005 STi w/ Throttle issues

Note: I posted this in the ECU area of the boards also because I, honest to God, have no idea what is causing this issue.

I have searched high and low for threads on numerous forums in an effort to find someone that's suffering from the same problem I've had for about 4 months now. Needless to say, I haven't found any.

Long story short:

-purchased used September 2010
-following parts installed May 2011 (and tuned via OpenSource)
1. DW 850cc Injectors
2. NGK one-step colder plugs
3. Hallman MBC
4. Cobb SF-intake / air box
5. Invidia v2 catless downpipe
6. Invidia G200 exhaust
7. Walbro 255lph fuel pump
-started having throttle issues December 2011
-primary O2 sensor replaced Jan 2012 (problem persists)
-cobb accessport purchased and installed (OpenSource tune converted to Accessport by my tuner) in order to datalog and hopefully determine the cause of throttle issue
-throttle body replaced March 2012 (problem persists)

The issue I'm having the part throttle surging. I've datalogged it and seen 'throttle position (%)' values go from 14.-- to 20.-- to 14.-- in a matter is a second, all while the accelerator position remains unchanged. After seeing such a variation in throttle position and talking with the mechanics and tuner, we figured it was the throttle body (possibly the servo taking a dump or the gears having too much play). Installed a new throttle body, still have the problem, but it doesn't seem to be quite to the extent that it was prior to changing it.

Worst part of it is I am throwing no codes and it is totally random. It only surges about 20% of the time and usually for no more than a minute or two at a time. The rest of the time it drives smooth as butter (I have datalogs showing that it CAN, in fact, maintain a constant throttle position).

If anyone has any ideas of what could cause this problem, please shoot them in my direction.

In the past few months, the problem seemed fairly minimal. Still slight surging, but nothing to the extent that it was. However, a couple of weeks ago, the problem came back with a vengeance. The battery mysteriously crapped out 2 weeks ago, so it has since been replaced. Hoping to get lucky and have it clear up the throttle problem, but no luck there. Light throttle, <40mph is generally pretty jerky (like the throttle is off and on in rapid succession). Freeway only seems to surge but may be cutting out slightly too (hard to tell in the higher gear). Cobb says they've never seen this issue before, but have seen free revs bounce around due to faulty injectors. The problem is really only while I'm on the gas. On rare occasion the revs will climb up to 2k or so while in neutral, but it's intermittent.

Honestly, I don't have any more ideas other than it possibly being a problem with my wiring harness or electrical components in the ECU are crapping out.

DOES ANYONE HAVE ANY IDEAS?!?! I am desperate at this point.

Thanks.

-Swede
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Old 05-25-2013, 08:39 AM   #2
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Take apart the throttle pedal, it's just a big potentiometer, it might be dirty. Also, did you make sure your dbw harness isn't pinched anywhere?
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Old 05-26-2013, 11:40 AM   #3
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Accelerator position doesn't change during the surges, indicating that the accelerator potentiometer is functioning correctly.

Haven't checked the DBW harness. I'll have to check it out when I have a chance.
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Old 05-26-2013, 05:17 PM   #4
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Man, I read the whole thing and missed that part. If the accelerator pos. isn't changing I'd suspect the tb or wiring. It might be the tb sensor, same deal for that too it's just a pot linked to the butterfly. Got any friends that'll lend you their tb? A known working one, unless the new one was brand new. Other than that intermittent means a short somewhere most likely.
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Old 05-27-2013, 12:21 AM   #5
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you mentioned above it can't be the accelerator because logs show that it doesn't change position. However, the wiring behind it (meaning after the sensor) may be causing an issue. It really sounds like a wiring problem to me, possibly dbw harness as you mentioned.

Have you tried moving the wiring around a bit and spacing it? If it only happens at low throttle input it could even be some em interference...have you done anything in that area as far as putting cables in? maybe gauges? or running a speaker wire?

Also, keep testing your battery with a voltmeter if you can... Test it after the car has been off for 10 or more hours and after a drive. If a wire is bad and touching something grounded it may be causing the issue. (I only mention all this since you said your battery was dead)
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Old 05-27-2013, 12:29 AM   #6
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oh, and this is a no brainer, but I assume you've checked ALL of your fuses ...sometimes they don't just blow...
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Old 05-27-2013, 12:52 AM   #7
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dbw relay? i believe its on the right side of the dash.
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Old 05-27-2013, 10:55 PM   #8
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Quote:
Originally Posted by dstroy View Post
Man, I read the whole thing and missed that part. If the accelerator pos. isn't changing I'd suspect the tb or wiring. It might be the tb sensor, same deal for that too it's just a pot linked to the butterfly. Got any friends that'll lend you their tb? A known working one, unless the new one was brand new. Other than that intermittent means a short somewhere most likely.
Throttle body is new. After seeing the fluctuations in throttle position, I suspected the throttle body gears had play in them. Replaced, still have the issue. I actually took the original throttle body apart and the gears were perfect.
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Old 05-27-2013, 10:59 PM   #9
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Quote:
Originally Posted by VictorOfHavoc View Post
you mentioned above it can't be the accelerator because logs show that it doesn't change position. However, the wiring behind it (meaning after the sensor) may be causing an issue. It really sounds like a wiring problem to me, possibly dbw harness as you mentioned.

Have you tried moving the wiring around a bit and spacing it? If it only happens at low throttle input it could even be some em interference...have you done anything in that area as far as putting cables in? maybe gauges? or running a speaker wire?

Also, keep testing your battery with a voltmeter if you can... Test it after the car has been off for 10 or more hours and after a drive. If a wire is bad and touching something grounded it may be causing the issue. (I only mention all this since you said your battery was dead)
Nothing has been installed since May 2011 (when the above mentioned after-market parts were installed) that isn't OEM. No speakers, no head unit, no gauges, nothing.

My old battery read fine on a voltmeter but had next to no cranking amperage (the reason why everything worked and the startup sequence worked just fine but the motor wouldn't start).
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Old 05-27-2013, 11:00 PM   #10
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Quote:
Originally Posted by teesutt View Post
dbw relay? i believe its on the right side of the dash.
I'll have to check this one out. Anyone have a location diagram for this?
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Old 05-27-2013, 11:09 PM   #11
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Cobb said they've seen fluctuations in RPM while trying to hold 2500 rpm in neutral that was caused by poor spray patterns in some fuel injectors. However, they did not log what the throttle body was doing during this. They said the spray pattern on the DW850s isn't the greatest, but I don't think this is what's causing my problem. If the throttle position wasn't changing EVERY time the problem occurs, this may be something to look at, but that's not the case for me.

I've tried this a couple of times in the past couple of days (after driving the car and having it drive like garbage) and haven't had any major fluctuations in RPM (other than very slight changes inherent to mechanical gauges).

I haven't checked the fuses, but I highly doubt any of them are blown since I'm receiving all the necessary voltages for everything in the car to function normally (other than the throttle body). Because it takes voltage to open the throttle body, it's hard to imagine that I would be shorting voltage TO that line, but I guess it's not out of the realm of possibility.
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Old 05-27-2013, 11:19 PM   #12
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Quote:
Originally Posted by SwedeSTi View Post
Cobb said they've seen fluctuations in RPM while trying to hold 2500 rpm in neutral that was caused by poor spray patterns in some fuel injectors. However, they did not log what the throttle body was doing during this. They said the spray pattern on the DW850s isn't the greatest, but I don't think this is what's causing my problem. If the throttle position wasn't changing EVERY time the problem occurs, this may be something to look at, but that's not the case for me.

I've tried this a couple of times in the past couple of days (after driving the car and having it drive like garbage) and haven't had any major fluctuations in RPM (other than very slight changes inherent to mechanical gauges).

I haven't checked the fuses, but I highly doubt any of them are blown since I'm receiving all the necessary voltages for everything in the car to function normally (other than the throttle body). Because it takes voltage to open the throttle body, it's hard to imagine that I would be shorting voltage TO that line, but I guess it's not out of the realm of possibility.
so, let's review...

With injector problems it wouldn't be a consistent rpm fluctuation, but rather much more sporadic and inconsistent which means it's probably electrical.

the reason I mentioned fuses is because previously I had a problem where while shifting right after WOT the engine would judder and shake before the clutch would grab again and go. It turned out to be a fuse related to my dbw throttle...it wasn't blown, in fact it looked immaculate, but changing it solved my problem...

your problem is so consistent it reminds of an issue that BMW used to have about 5 or 6 years ago, but that was related to overused coils and sparkplug problems. (the ones i saw would rev to 4k then down to 2 then 4 again similar to yours)

As someone mentioned the relay might be the problem, but also with this consistency I would try a retune maybe? or possibly replace the sensor for the throttle and/or clutch. I don't know about your model as much as my own, but in mine the ecu knows when the clutch and throttle are both down/up which can cause judder problems like I had or maybe even this.

I'm no expert on your model by any account, but I would check those just in case
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Old 05-27-2013, 11:25 PM   #13
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Quote:
Originally Posted by teesutt View Post
dbw relay? i believe its on the right side of the dash.
upon some reflection, a bad capacitor or voltage modulator within the relay could very very well be causing this issue...

car electrical problems, curse you!!
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Old 05-28-2013, 01:00 PM   #14
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I know that if you pull the relay the throttle has 0 response. I swapped a 04 sti drivetrain and harness into an 05 wrx. didnt know about the relay until we got everything swapped and had no throttle. Obtained a wiring schematic, $20 at the dealership and problem solved.

Its definitely worth looking at. #2 in the diagram.


Last edited by teesutt; 05-28-2013 at 02:19 PM.
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Old 05-31-2013, 06:30 AM   #15
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Quote:
Originally Posted by VictorOfHavoc View Post
so, let's review...

With injector problems it wouldn't be a consistent rpm fluctuation, but rather much more sporadic and inconsistent which means it's probably electrical.

the reason I mentioned fuses is because previously I had a problem where while shifting right after WOT the engine would judder and shake before the clutch would grab again and go. It turned out to be a fuse related to my dbw throttle...it wasn't blown, in fact it looked immaculate, but changing it solved my problem...

your problem is so consistent it reminds of an issue that BMW used to have about 5 or 6 years ago, but that was related to overused coils and sparkplug problems. (the ones i saw would rev to 4k then down to 2 then 4 again similar to yours)

As someone mentioned the relay might be the problem, but also with this consistency I would try a retune maybe? or possibly replace the sensor for the throttle and/or clutch. I don't know about your model as much as my own, but in mine the ecu knows when the clutch and throttle are both down/up which can cause judder problems like I had or maybe even this.

I'm no expert on your model by any account, but I would check those just in case
Plugs were changed when the parts were installed, so they've got less than 15k on them. I drove on the tune that is currently loaded for months before this issue came about and have since been back to my tuner for verification. He rode in the car with me for about 45 minutes (throttle never fluctuated - murphy's law), but said everything with the tune looks good. Cobb has looked at the tune and said the same thing.
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Old 05-31-2013, 06:31 AM   #16
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Quote:
Originally Posted by teesutt View Post
I know that if you pull the relay the throttle has 0 response. I swapped a 04 sti drivetrain and harness into an 05 wrx. didnt know about the relay until we got everything swapped and had no throttle. Obtained a wiring schematic, $20 at the dealership and problem solved.

Its definitely worth looking at. #2 in the diagram.

thanks for the diagram. I will look into the relay. By the sounds of it, depending on what is inside this relay, this may be the culprit. At least I'm for damn sure hoping it is...
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Old 05-31-2013, 07:41 AM   #17
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Originally Posted by teesutt View Post
I know that if you pull the relay the throttle has 0 response. I swapped a 04 sti drivetrain and harness into an 05 wrx. didnt know about the relay until we got everything swapped and had no throttle. Obtained a wiring schematic, $20 at the dealership and problem solved.

Its definitely worth looking at. #2 in the diagram.

You wouldn't happen to have a part number for the throttle relay, would you? I've tried looking on SubaruGenuineParts.com but can't find this relay (or the fuel pump relay, for that matter), and their online catalog doesn't show parts breakdowns or part numbers.

I was reading on another board about a throttle problem a guy was having in his Forester that sounded like it is somewhat similar to this problem. I would imagine the drive by wire systems are pretty similar between the models, so this definitely has some potential.

Last edited by SwedeSTi; 05-31-2013 at 07:48 AM.
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Old 05-31-2013, 09:45 AM   #18
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Dont know the part number. If you have a dealership by you, stop in and have the parts department look it up.
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Old 05-31-2013, 12:19 PM   #19
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Have you ruled out a vacuum leak? Had a friend locally that chased similar for two years, finally found a vacuum leak in the evap hoses.
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Old 05-31-2013, 02:26 PM   #20
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Had the similar problem a few months ago. On a long trip at constant speed there was noticeable surging. I found out that it could be a sign of O2 sensor going bad, but i didnt get any CELs. After a couple of months of checking spark plugs, coils, vacuum lines, mass air flow sensor, injectors and everything else that could contribute to the problem I finally got a CEL for bad O2 sensor. Replaced it and the problem is gone.
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Old 05-31-2013, 11:49 PM   #21
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Primary O2 sensor was one of the first things replaced after this problem started. Cobb suggested a possible vacuum leak, but I haven't had a chance to go through the lines to check and/pressure check the intake system.

I'm taking an educated guess that datalogs would show different fluctuations if it were a vacuum leak. I would be struggling to maintain steady a/f ratios if a vacuum leak were present because the ECU would constantly be adding/pulling fuel to compensate for the unmetered air in the system. Not only that, I don't think a vacuum leak would have any effect on throttle position. I could be wrong, but the only thing that should affect throttle position is accelerator input. Based on the fact that nothing else is changing, the throttle relay sounds like the most likely culprit. If I am mistaken, please correct me.

The service department at the Subaru dealership is going to look up the relay part number for me on Monday when they open.

I will post a couple of logs when i get home that I've taken that illustrate exactly what's going on. Does anyone have a factory service/repair manual for an '05 STi? Or at least have experience with one that is commercially available so I can try to purchase one? I see a couple different manuals in eBay available on cd but I'm unsure if they're all the same or one is better than another.
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Old 06-01-2013, 01:30 AM   #22
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Quote:
Originally Posted by SwedeSTi View Post
Primary O2 sensor was one of the first things replaced after this problem started. Cobb suggested a possible vacuum leak, but I haven't had a chance to go through the lines to check and/pressure check the intake system.

I'm taking an educated guess that datalogs would show different fluctuations if it were a vacuum leak. I would be struggling to maintain steady a/f ratios if a vacuum leak were present because the ECU would constantly be adding/pulling fuel to compensate for the unmetered air in the system. Not only that, I don't think a vacuum leak would have any effect on throttle position. I could be wrong, but the only thing that should affect throttle position is accelerator input. Based on the fact that nothing else is changing, the throttle relay sounds like the most likely culprit. If I am mistaken, please correct me.

The service department at the Subaru dealership is going to look up the relay part number for me on Monday when they open.

I will post a couple of logs when i get home that I've taken that illustrate exactly what's going on. Does anyone have a factory service/repair manual for an '05 STi? Or at least have experience with one that is commercially available so I can try to purchase one? I see a couple different manuals in eBay available on cd but I'm unsure if they're all the same or one is better than another.
I agree with you there. small leaks don't often show, but larger ones that could cause this would and they wouldn't be so consistently accurate on the rev pattern you're seeing...

consistency to me means electrical issues 90% of the time
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Old 06-01-2013, 05:47 AM   #23
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Son of a bitch. I just typed out this whole thing using values I've seen in some of the logs I've done, hit post reply, and the damn forums were down so I lost it all.

Let's try this again...

I lied about posting datalogs; I do not have the proper clearance to post attachments on the boards. If anyone is interested in seeing the actual logs I will have to email them. I have a few that illustrate the problem pretty well.

For now, I'll explain as best I can:

For a baseline, I have a log that shows the accelerator position held steady at 10.98% for the duration of the 41-second log. Throttle position holds steady at 15.29% the entire time (less an occasional drop to 14.9%). This is normal and is how the throttle should react all the time.

Now for the crap:

In a log I did on request from Cobb Tuning, accelerator position holds steady at 11.76%. Throttle position, on the other hand, varies anywhere from 10.2% to 16.86%. A little more interesting, in 5 consecutive cells (less than a half-second on this log), throttle position changes from 13.33% to 10.98%, back to 13.33%, then to 10.2%, and then to 13.73%. That's just a quick look at the log without scouring it.

The most drastic variation in throttle position I've managed to log was from 4 March 2012. With accelerator position steady at 12.55%, throttle position starts at 15.69%, drops to 12.16%, surges to 20.39%, then back to 15.69%...all in a matter of a second and a half (4 consecutive cells in this log).

This variation, even though it's only a couple of percent, is felt while driving. The car will buck and lunge. Not only that, I can watch the changes on the boost gauge, indicating to me that the throttle plate IS moving (more gas isn't going to increase manifold pressure, it will only increase a/f ratios).

Cobb told me that the spray pattern for the DW850s isn't the greatest, and they've seen faulty injectors cause variation in RPM during free-revving conditions (i.e. trying to hold 2500rpm in neutral). I've tried this on multiple occasions and have no issues maintaining a steady RPM in neutral. I've tried moving the wire bundles that I can see (inside the car and in the engine bay) with the car running with no change in how it runs (doesn't surge or die). And like I said in an earlier post, a vacuum leak shouldn't have any effect on throttle position.

Needless to say this has been a giant PITA for about a year and a half. It isn't all the time, and I have no idea what causes it, but it has gotten worse in the past few weeks. Luckily, I don't need to drive it much, but I would still like to get to the bottom of this because it is damn irritating when I do have to drive it. Worst part about the whole thing: no CEL!

At one point I thought it may have been temperature related (seemed to happen while it was colder outside), but that was blown out of the water when it was about 95 degrees and started do the same thing. I haven't gotten any logs for a while, so I will try to get out this weekend and get a couple of logs and see if there are any changes.
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Old 06-01-2013, 07:42 AM   #24
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Post on google docs, make pubkic w/ link (share.) Post link here.
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Old 06-02-2013, 04:41 PM   #25
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datalogs uploaded to google docs:

Baseline throttle (proper operation): https://docs.google.com/spreadsheet/...kE&usp=sharing

Consistent variation throughout log: https://docs.google.com/spreadsheet/...Wc&usp=sharing

Significant throttle change: https://docs.google.com/spreadsheet/...3c&usp=sharing

These 3 logs represent the three I mentioned in my previous post.
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