Rough idle and stall only when stopped.

Posts specific to the 2.0 litre Turbo engine

Rough idle and stall only when stopped.

Postby auzzi3 » Sun Feb 15, 2015 9:16 pm

hey guys im new to this forum and ive owned my suabru liberty 2004 turbo 2.0l for 8 months..

since ive owned it ive had a 02 sensor fault code on my ecu.. ive never had any issues and had no time to fix it..

well my issue is:
last week i was driving and suddenly began to feel sluggish and rough on idling..
the next day every time i stop it, or pull up to lights it wants to stall.. it shakes dramatically.. and when i take of its sluggish until i hit 2k revs then it drives fine..

i had the spark plugs changed,
ive had a fuel pressure test and that was fine
i had a vacuum test done.. it was fine under load but abnormal on idle..

im wondering if any one has had the same issue and if so what actions to take first as i dont want to spend large amounts of my to diagonose.

thx guys.,
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Re: Rough idle and stall only when stopped.

Postby KiDo_Tuning » Mon Feb 16, 2015 12:19 am

auzzi3 wrote:hey guys im new to this forum and ive owned my suabru liberty 2004 turbo 2.0l for 8 months..

since ive owned it ive had a 02 sensor fault code on my ecu.. ive never had any issues and had no time to fix it..

well my issue is:
last week i was driving and suddenly began to feel sluggish and rough on idling..
the next day every time i stop it, or pull up to lights it wants to stall.. it shakes dramatically.. and when i take of its sluggish until i hit 2k revs then it drives fine..

i had the spark plugs changed,
ive had a fuel pressure test and that was fine
i had a vacuum test done.. it was fine under load but abnormal on idle..

im wondering if any one has had the same issue and if so what actions to take first as i dont want to spend large amounts of my to diagonose.

thx guys.,


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Re: Rough idle and stall only when stopped.

Postby auzzi3 » Mon Feb 16, 2015 5:34 am

Liverpool nsw
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Re: Rough idle and stall only when stopped.

Postby bigBADbenny » Mon Feb 16, 2015 8:37 am

My advice would be to reach out to a local member (or e-tuner) with a Tactrix or btSsm device.

Then get the CEL code read, take a learning view, and do a log of general driving and idling with the usual parameters plus VVT inlet and exhaust angles.

Replace the relevant 02 sensor with a genuine item via Garage88 or online.
Look for further issues in the logs and LV.
A good e-tuner can also help diagnose issues if you choose to get the car tuned - it can be a cost effective option with side benefits to economy and drivability.

At the same time it would be easy to DIY go over the basics like: (see the pre tune faq link in my sig)
Cleaning the MAF and airfilter,
Checking the condition of the in tank -fuel filter, replacing it if required, and replacing or upgrading the fuel pump.
Use some Subaru fuel additive and just before the next oil change using UEC in the oil and BOV vac tube.
Do the boost and vac check on the inlet, tmic and the exhaust on cold startup.
Then the coil packs and plugs could be checked at the same time.
Checking battery voltage at idle and in normal warmed up driving, checking the alternator belt tension.

Here's some more reading: https://www.google.com/search?q=Rough+i ... 8&oe=utf-8
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Re: Rough idle and stall only when stopped.

Postby alexeiwoody » Mon Feb 16, 2015 11:48 am

Sounds like a vac leak (check all the vac lines are on, they tend to come off often), but you'd want to replace the O2 sensor first if the CEL is flashing.

As Benny said, a quick learning view (software program off RomRaider.com + tactrix cable to connect laptop to car) will show if you've got a vac leak and/or o2 sensor problem.
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Re: Rough idle and stall only when stopped.

Postby KiDo_Tuning » Mon Feb 16, 2015 4:58 pm

I am happy to help with a diagnosis at no cost. Its easier than trying to diagnose over the internet :)

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Re: Rough idle and stall only when stopped.

Postby auzzi3 » Wed Feb 18, 2015 11:16 pm

Hey mate. I would really appreciate that if you are still offering. Thx man im not the biggest car enthusiast and your knowledge would help alot To find my fault. Let me know thank you
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Re: Rough idle and stall only when stopped.

Postby auzzi3 » Thu Feb 19, 2015 2:37 pm

Also.. my steering is much heavier at times.. any ideas guys? My power steering fluid is full. Thx ps still havent rectified the problems.
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Re: Rough idle and stall only when stopped.

Postby teh_mechanic » Sun Feb 22, 2015 9:38 am

You say the vacuum was abnormal at idle (high vacuum point) but OK at load (low vacuum point), this and your symptoms of rough idle and stalling etc are consistent with a vacuum leak after the throttle body, or an intake tubing leak after the MAF (Mass airflow sensor) before the throttle body - either of these allows air to be sucked in after the MAF , ruining your fuel injection calculations. So that's where I'd start your diagnosis.

Have a look around the intake manifold for any obvious hoses popped off, if it's a large enough a leak to cause stalling you will probably be able to track it down by the hissing noise it makes. Next option, use a spray bottle of water and mist it around the manifold, listening for any change in RPM as the water gets sucked into the leak. Ensure your intake piping tube isn't split. Last, foolproof option for air leaks, is to have a garage with a smoke machine to smoke test the intake system.

Regarding the 02 sensor code. A vacuum leak will cause a very lean fuel condition, which can cause innactivity with the 02 sensor, enough for it to set a code. So I wouldn't just go replacing the 02 sensor yet as it may be a knock on effect of the actual problem. It will come down to the actual P code being set for the 02 sensor ie. a P0141 02 sensor heater circuit malfunction code has nothing to do with anything else, it's just very likely your 02's heater is dead, whereas a P0131 02 sensor low voltage code is often set by a good working sensor that is producing low activity because of a real engine/fueling problem, eg a lean condition from a vacuum leak.
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Re: Rough idle and stall only when stopped.

Postby alexeiwoody » Sun Feb 22, 2015 10:07 am

teh_mechanic wrote:You say the vacuum was abnormal at idle (high vacuum point) but OK at load (low vacuum point), this and your symptoms of rough idle and stalling etc are consistent with a vacuum leak after the throttle body, or an intake tubing leak after the MAF (Mass airflow sensor) before the throttle body - either of these allows air to be sucked in after the MAF , ruining your fuel injection calculations. So that's where I'd start your diagnosis.

Have a look around the intake manifold for any obvious hoses popped off, if it's a large enough a leak to cause stalling you will probably be able to track it down by the hissing noise it makes. Next option, use a spray bottle of water and mist it around the manifold, listening for any change in RPM as the water gets sucked into the leak. Ensure your intake piping tube isn't split. Last, foolproof option for air leaks, is to have a garage with a smoke machine to smoke test the intake system.

Regarding the 02 sensor code. A vacuum leak will cause a very lean fuel condition, which can cause innactivity with the 02 sensor, enough for it to set a code. So I wouldn't just go replacing the 02 sensor yet as it may be a knock on effect of the actual problem. It will come down to the actual P code being set for the 02 sensor ie. a P0141 02 sensor heater circuit malfunction code has nothing to do with anything else, it's just very likely your 02's heater is dead, whereas a P0131 02 sensor low voltage code is often set by a good working sensor that is producing low activity because of a real engine/fueling problem, eg a lean condition from a vacuum leak.


Good detailed advice :)
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Re: Rough idle and stall only when stopped.

Postby KiDo_Tuning » Mon Feb 23, 2015 11:54 am

Issue resolved. Front passenger side intake AVCS solenoid was blocked in the open position. Had full oil flow at idle so was stuck on 52 degrees advance. No dynamic compression on one side of the engine, result was 2 cyl boxer motor at idle and poor vacuum. Uncombusted fuel was being blown out the exhaust port and causing an O2 sensor heater issue and code as the twinscroll housing prevented 'ignition' of the passenger bank until post turbo or right where the O2 sensor is.

5 minute fix thankfully and sorted
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Re: Rough idle and stall only when stopped.

Postby bigBADbenny » Mon Feb 23, 2015 12:52 pm

Nice one ;)
Did you remove and clean the OCV on the spot?
Actuate it whilst cleaning?
Or was it easier than that?
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Re: Rough idle and stall only when stopped.

Postby teh_mechanic » Wed Feb 25, 2015 8:43 pm

Nice one, VVT issues have been on the rise across all makes in our shop but they all have one thing in common, poor service history.

Keep up those oil changes guys.
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Re: Rough idle and stall only when stopped.

Postby bigBADbenny » Wed Feb 25, 2015 10:15 pm

It's absolutely the main factor but 2.5t's seem to get ocv issues regardless of service history.
Perhaps the factory oil change interval is optimistic.
Maybe ocv's should be a 100k service item.

At any rate it's worth investing in a btSsm and or a Taxtrix, or reaching out to a local with that facility for the occasional health check :)
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Re: Rough idle and stall only when stopped.

Postby DanKatt » Wed May 13, 2015 3:43 pm

KiDo_Tuning wrote:Issue resolved. Front passenger side intake AVCS solenoid was blocked in the open position. Had full oil flow at idle so was stuck on 52 degrees advance. No dynamic compression on one side of the engine, result was 2 cyl boxer motor at idle and poor vacuum. Uncombusted fuel was being blown out the exhaust port and causing an O2 sensor heater issue and code as the twinscroll housing prevented 'ignition' of the passenger bank until post turbo or right where the O2 sensor is.

5 minute fix thankfully and sorted


Hey Kido, do you have a procedure/photos to follow of how to clean the AVCS solenoid? I have seen this mentioned a few times in differnet threads and i'm having similar issues to auzzi3.
My car was idling rough, but ok to drive so i replaced O2 sensor, had injectors cleaned, upper engine clean, AFM clean, and a vac test which showed up quite a few leaks which have all been sorted.
The car runs well now, but it has the occasional engine shutter when stationary, usually when engine is warm or after a bit of a squirt, and the fuel usage is very high (around 14L/100) even after normal city driving.
So i'm thinking either the fuel filter needs replacing (fairly straight forward) or the solenoid is blocked, but I'm not sure where this is, or what to look for.
Also do you think a flash tune could help?

Any advice would be appreciated. Cheers
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