2008 Outback low idle stalls

[MaryB 12]

Need some help after our actions did not fix the problem:

 

Outback got an oil change and check before a trip in September, at 135K miles. For the first time I experienced the car not shifting into lower gear when accelerating up a hill on the highway. The RPMs went up, but no downshift. I slowed down and the problem did not return.

 

Two weeks later the car died at idle in drive on an incline and threw code p0028. Car started idling rough at a stop or when in reverse at very low speed. Sometimes it died but restarted fine. We found some moisture in the spark plugs and tried removing. Ended up breaking a wire so we took it to our trusted mechanic for new plugs and wires.

 

After that the car performed well for two weeks until last week on a trip in the foothills. Threw the p0028 code while on a straightaway, but the idle problem did not return like before.

 

We cleared the code and chose to install a new variable valve timing control solenoid. We also cleaned the switch. The code is gone but the car is again idling rough and sometimes dying at idle in drive or reverse. Today we put in a new switch. Husband confirmed switch and solenoid are opening properly. But no change to our rough idle. We drove it around the block, it did not throw a code.

 

What is our next best option?

Edited October 11, 2017 by MaryB

[1 Lucky Texan 1048]

my first concern would e that fluid drain/fill was confused. You need to triple check trans a dn engine oil levels and 'quality' of fluid. The trans is checked while idling.

[MaryB 12]

confused? We checked these items in September. Engine oil level is full. Transmission oil was replaced about this time last year and is good.

[1 Lucky Texan 1048]

If you shift into N before stopping, would the car die? maybe the TC is not releasing.

 

have there been any other codes retrieved?

 

were OEM/NGK parts used when plugs and wires were installed?

 

when idling poorly, you could try squirting some starter fluid in the intake. If it smooths-out, that could indicate a fuel problem.

 

Live data may be required to pinpoint the problem.

 

is the car new to you? did the car get it's timing belt system service 30K miles ago?

[GeneralDisorder 1791]

When the switch is at fault for a P0028 It virtually never causes any kind of rough idling. Replacing the switch generally fixes that code in 99.99% of cases I've seen. 

 

Rough idle is likely unrelated to the code. Find out which cylinder is misfiring. Unplug injectors till you find the one that doesn't cause any change in idle speed, etc. When you find the cylinder that's not firing inspect all the ignition components carefully.

 

GD

[MaryB 12]

will ask for cylinder inspection this Friday at trusted mechanic's shop, along with ignition component checks. Husband believes this is an ignition component problem too.

 

Timing belt replaced two years ago, at 108K miles. Transmission fluid and radiator is < 1 year old.

 

OEM spark plugs and wires, installed by trusted mechanic, and symptoms disappeared after mechanic installed new plugs and wires.

 

Shifting to N causes the idle to rise a bit and steady's it out to be smooth, and does not stall out.

 

No other codes to report. We've owned this car since August 2015.

Edited October 11, 2017 by MaryB

[MaryB 12]

doing additional internet research and came across a 2008 Legacy with the same symptoms: p0028 and rough low idle

 

 

I’ve driven the car for 450 miles so far and nothing drastic has happened, I can hit high speeds no problem. There has been times where
if i press on the gas hard to accelerate and the RMPs shoot up but the car gains speed slowly, Im afraid so I just don’t do that anymore. Andy

 

 

Hello Andy,

I would start with a oil change with good oil and a Great Filter,
from there if the problem persists most likely it needs a solenoid or
two.

9 times out of ten we find that it has a cheap oil filter causing all of the issues.

We have corrected these codes on many Subaru vehicles with just an oil change. But we have also found scored cylinder heads from
repeatedly stretching out the oil changes to far ultimately be the culprit as well, I just based on the info you can’t give me know the
exact cause from here, but what the ECM is seeing is insufficient Cam shaft timing advance under load when it sets those codes.

Hope that helps

-Justin

 

This guy also suggested rough idle/stuttering is now showing up on 2.5 engines like ours and suggests “dropped” exhaust valve guides

[GeneralDisorder 1791]

Yes dropped valve guides is common on that year. It requires replacement of the cylinder head. The heads are cracked which leads to the guides shifting. I believe there are revised heads to address the issue. No recall though.

 

The poster that you quoted has an insufficient understanding of the system though as he mentions camshaft (valve) timing advance and these engines do not have variable valve timing. What they have is variable valve LIFT and changing the valve lift in and of itself generally will not cause a drastic change in idle quality. 

 

Poor oil and filter and infrequent oil changes definitely can affect the system though and isn't good for the engine for sure. These engines need FULL synthetic and high quality filters (WIX, Amsoil, etc) or they end up living a short and smokey life. 

 

GD

Edited October 11, 2017 by GeneralDisorder

[MaryB 12]

thanks for that clarification. When I found that description matching mine (rpms shoot up, p0028 code) I was hopeful someone else diagnosed what I am experiencing. Oh well.

[MaryB 12]

and now it is time to mention my husband changed the oil and filter out before our September trip. I will ask what oil and filter was used. If he did not go with synthetic and high quality filter I will suggest doing so today.

[MaryB 12]

He replaced the oil with Napa brand and Wix-made Napa brand oil filter.

[GeneralDisorder 1791]

Napa synthetic or dino oil? If synthetic it's probably ok but not ideal. If it's dino oil then that is absolutely not good for the engine long term. 

 

GD

[MaryB 12]

mechanic found an air leak at the hose going in to the air induction system, affecting the MAF. The hose was installed in the wrong configuration, allowing a crack for air to get inside. It's a big 4" tube. To be clear the symptoms started before he replaced the spark plugs a few weeks ago. We really don't know why the problem presented it the way that it did.  He fitted the hose correctly and tightened the clamp. That's it. There were no other codes. Test drive was smooth and wonderful. Yay.

[GeneralDisorder 1791]

Nice. Yes a metered air leak will cause l kinds of problems. 

 

GD