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Discussion Starter #1
Hi!

I've been having a headache over my 2.5 Outback 5mt for a long time now and have searched and searched and tried different things without success. I finally thought I would give it a try and ask here. I really hope someone can point me in a direction because it is driving me mad!

Symptoms:
-Idle to low after fully warm up. Idle is steady RPM wise but now and then there is a light shake (misfire?) and popping from the exhaust. Idle sounds weak.
-At low throttle (in idle) the RPM goes up and then down again without me releasing the throttle. Then up. Then down. This makes for a bumpy ride in gear at low speed.
-When the throttle is released at higher RPM, there seems to be a "blablablabla" sound coming from the exhaust (to rich?). RPM then dips, almost stalling but goes back up again after a second.
-Exhaust fumes. They look normal but I have noticed that they are visible even after the car is warm for a long time (every time). There is also, perhapse, a slightly "gassy" smell to them. But I do not know this car from before so can't compare.

What I have tried so far:
-Checked codes, no codes.
-Did multiple idle relearns.
-New timingbeltkit, waterpump, coolant (it was time for it anyway).
-New sparkplugs, oil, airfilter. Sparkplugs looked good (very light brown).
-Checked many times for vacuum leaks. Can't find any.
-New front o2 sensor.
-Tested swapping the MAF with a used one. No difference.
-Removed and cleaned PCV and EGR. They seemed fairly clean and PCV was clicking as it should. Some oil in the PCV hose but that's normal i guess.
-Removed and cleaned throttlebody. Was dirty and there was alot of oil in the intake. Cleaned it really well but no difference in performance after.
-Measured battery volts (12.7 with car off) as well as volts between battery neg.terminal and various ground sources with headlights on. Everything seemed fine (max. 0.3 v).

Car starts fine and runs well until fully warm. Also seems to run fine at highway speeds and when accelerating hard.

Any hints are very appreciated!

Best,
Zach
 

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2012 OB , 2017 Impreza
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You say that you have checked for codes so I assume you have a code-reader. If it has ability to read 'realtime' data, monitor
*) MAF sensor (Grams/Second)
*) Long Term fuel Trim (LTFT)
*) Short Term fuel Trim (STFT)

The MAF should read between 4g/s and 7g/s at idle
Add the LTFT and STFT together.... (should be near 0)

Tell us the results.
 

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Have you checked the IAC Valve and o-ring? A vacuum leak would cause all the symptoms. On my car, it seemed to take a while before code P1507 popped.
 

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Discussion Starter #4
You say that you have checked for codes so I assume you have a code-reader. If it has ability to read 'realtime' data, monitor
*) MAF sensor (Grams/Second)
*) Long Term fuel Trim (LTFT)
*) Short Term fuel Trim (STFT)

The MAF should read between 4g/s and 7g/s at idle
Add the LTFT and STFT together.... (should be near 0)

Tell us the results.
Will check it and get back!
Have you checked the IAC Valve and o-ring? A vacuum leak would cause all the symptoms. On my car, it seemed to take a while before code P1507 popped.
Thank you, my car has an electronic throttle body though so no IAC.
 

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Have you checked the IAC Valve and o-ring? A vacuum leak would cause all the symptoms. On my car, it seemed to take a while before code P1507 popped.
This is EXACTLY why I suggested monitoring MAF, STFT and LTFT. A vacuum leak would be VERY easy to spot if the fuel-trims are not near 0.
 

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This is EXACTLY why I suggested monitoring MAF, STFT and LTFT. A vacuum leak would be VERY easy to spot if the fuel-trims are not near 0.
Is 6-8% LTFT "normal", or could that indicate a potential vacuum leak? I recently bought a smoke machine and smoked the intake. There was quite a bit of smoke coming out around the EGR valve. Enough so I couldn't see exactly where it was coming from. The problem is that my smoke machine isn't pressure regulated and is capable of pushing over 20psi, so I was thinking a leak around the EGR valve stem might be normal under those conditions.
 

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Is 6-8% LTFT "normal", or could that indicate a potential vacuum leak? I recently bought a smoke machine and smoked the intake. There was quite a bit of smoke coming out around the EGR valve. Enough so I couldn't see exactly where it was coming from. The problem is that my smoke machine isn't pressure regulated and is capable of pushing over 20psi, so I was thinking a leak around the EGR valve stem might be normal under those conditions.
This is an interesting subject.
However.... Please do not 'hijack' this thread to discuss issues with your vehicle. Instead, consider starting your own discussion so it can be kept seperate from Zen04.
 

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This is an interesting subject.
However.... Please do not 'hijack' this thread to discuss issues with your vehicle. Instead, consider starting your own discussion so it can be kept seperate from Zen04.
I don't need you to explain forum etiquette to me like I'm some child. My intention wasn't to 'hijack' this thread. I figured the info could be relevant to OPs problems since they're similar to mine. Sorry to bunch your panties.
 

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Discussion Starter #10
I'm thankful for all your replies and thoughts! Here are some data. This is on idle with the engine fully warm up. I have to make a correction though; I said 2.5 but meant 2.0...I also have a 3.0 so I mix them all up sometimes haha. But this is a 3rd gen 2.0 Outback sport/XV with the EJ20 (NA). That may explain the slightly lower AFR perhapse. I know that you don't have this engine in America but they are very similar to the 2.5.

508280


508281
 

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Nice job collecting the data!! (y) (warm engine at idle)

Some observations:
  • The system has achieved closed loop operation.
  • The 'wide range O2' reading being 0.997 is very close to the 1.00 that the computer tries to achieve.
  • The LTFT b1 being negative suggests there is NOT a vacuum-leak. (and perhaps even running a bit rich)
  • The STFT b1s2 being positive the EXACT same amount is interesting. (perhaps ECU is compensating for something?)
Be aware that sensor1 is BEFORE the catalyst and sensor2 is AFTER the catalyst.
Perhaps a catalyst efficiency test would help isolate the running issues you are describing?

You may even have a failing O2 sensor.
In some cases, graphing the outputs of the O2 sensors will show the response and function of the O2 sensors.

Often a graph 'capture' of sequence: idle - rev and hold - back to idle can be useful.
May answer the questions:
  • Are the O2 sensors responding appropriately?
  • Is the catalyst doing its job?
 

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Discussion Starter #12
Nice job collecting the data!! (y) (warm engine at idle)

Some observations:
  • The system has achieved closed loop operation.
  • The 'wide range O2' reading being 0.997 is very close to the 1.00 that the computer tries to achieve.
  • The LTFT b1 being negative suggests there is NOT a vacuum-leak. (and perhaps even running a bit rich)
  • The STFT b1s2 being positive the EXACT same amount is interesting. (perhaps ECU is compensating for something?)
Be aware that sensor1 is BEFORE the catalyst and sensor2 is AFTER the catalyst.
Perhaps a catalyst efficiency test would help isolate the running issues you are describing?

You may even have a failing O2 sensor.
In some cases, graphing the outputs of the O2 sensors will show the response and function of the O2 sensors.

Often a graph 'capture' of sequence: idle - rev and hold - back to idle can be useful.
May answer the questions:
  • Are the O2 sensors responding appropriately?
  • Is the catalyst doing its job?
Gold, thank you! I will get to it, collecting some more data on the O2 sensors!

When you say that my o2 sensor may be failing, you are referring to the rear one, correct?
 
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