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Registered
2001 Outback, 2.5L auto
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2 Posts
Discussion Starter #1
Good day - First post to this forum, I'm hoping there is a magician...

I've an 01 Outback, which has been suffering with a random stutter during / off of idle. I'll be hanged if I can find it (nor can the shop I took it to)... The vehicle has ~105K. Currently, there are no codes recorded.

I cannot say it is dependent on the engine or the ambient temperature - seen it both cold and hot. It's been on-going for a couple of years - comes and goes, but is progressively getting worse.

The best way that I can describe this is the behavior seen with carburetor icing in an older vehicle - that or a mis-adjusted choke. Off of a start, or at low throttle/idle, the engine stutters and runs rough - like it's not getting proper fuel. This is improved with heavy throttle, or higher RPM.

I have had a bad knock sensor, and replaced this - cleared codes and none have returned. The hesitation was not dependent on this - it occurred both before and after replacement of the sensor.

I have removed and cleaned the idle air control valve.

I have removed and bench cleaned the injectors with BG injector cleaner. The spray is finely atomized, and the injectors all work well.

I have replaced the air and fuel filters.

I read Tim's posts (www.subaruoutback.org/.../19343-hesitation-stuttering-loss-power.html) - this is similar, but I have no codes...

Any ideas? I'm stumped. Possible to have a bad O2 sensor without a code?
 

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Premium Member
01 VDC, 05 R Sedan, 06 BAJA EJ257
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15,487 Posts
"Possible to have a bad O2 sensor without a code?" Yes.

Do you have access to a scan tool that reads data? If so, there is an example of O2 sensor outputs with a proper running H4 in my thread http://www.subaruoutback.org/forums/66-problems-maintenance/49537-p0420-diag.html . The one I had to put a CAT in.

Also, have you checked the ECT output to the computer? Checked the TPS function? Cleaned the throttle body? Checked and cleaned all the ground lugs and battery cables? Checked for vacuum leaks? Exhaust leak?

Outside the engine performance, there's the front axles, transmission fluid condition effecting the torque converter or mounts causing vibrations.
 

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Registered
2009 Tribeca Now - 2004 Outback EJ259 - Sold
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1,069 Posts
My money is on something engine mechanical.
One or more walked exhaust valve guides, carbon build up/lack of maintenance causes the valve to pull out the guide.
Over time the engine stumbling becomes worse, valve exhibits all kinds of strange behavior, sticking, not fully seating, ect...
Never throws an engine code but causes all kinds of engine stumbling, rough running, generally higher rpm's mask it.
See them quite a bit on all models, even up to 09'.
A couple guides I have done came out of the heads so far it pops the oil seal off the stem, lots of oil gets dumped into the exhaust at that point.

Compression test should show you how many cylinders are affected.
or if you want too see it
Take the exhaust manifold off and have a look with a flashlight, only takes a few minutes.
Have yet too see it on the intake side yet.

No luck finding a photo of it, did find a video though.
 

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Registered
2001 Outback, 2.5L auto
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2 Posts
Discussion Starter #4
Thanks for the quick replies -

Cardoc - I do not have a datalogger - this is on my list, but pricey for the times I'd use it...
- have you checked the ECT output to the computer? Only mechanically - would this not throw MIL?
- Checked the TPS function? no - this has been one of areas I have thought might be the culprit - seems if I'm in neutral, and I 'blip' the throttle, the return is to 'normal' idle.
- Cleaned the throttle body? yes
- Checked and cleaned all the ground lugs and battery cables? yes
- Checked for vacuum leaks? yes
- Exhaust leak? yes

"Outside the engine performance, there's the front axles, transmission fluid condition effecting the torque converter or mounts causing vibrations." New half shafts a month ago, with lower ball joints. Tranny has been flushed (BG power flush) and refilled within 5K miles.

NTIPPET - Thats one I haven't heard/thought of. Had the valve covers off last spring to replace the oil seals on the plug wires, and didnt see anything odd. I'll run compression checks, although maybe not today - it's below zero....
 

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2009 Tribeca Now - 2004 Outback EJ259 - Sold
Joined
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1,069 Posts
You might be able to see the valve guide height differences with the valve covers off, but I doubt it.
They are kind of buried, you would have to look past the rockers/camshaft cap then through the small gaps in the valve springs, maybe a couple small mirrors could help.
Much easier to do it through the exhaust ports, take the manifold off and they are staring at you.
 

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Premium Member
01 VDC, 05 R Sedan, 06 BAJA EJ257
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15,487 Posts
If you have a laptop, RomRaider and FreeSSM software is free and there are options for the OBDII access cable. Some use the VAG cable, I use Tactrix specific to Subaru. Either way, its more cost effective than paying a shop a diagnostic fee and the results from data logging can be posted on a this forum for those of us experienced in reading the data to help you find the issue.
 
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