Rough Idle & Engine Shaking under load like AC

[ilib11]

Hi All,
Got some issues after a dealership did a service and disconnected the battery.... need your collective knowledge to understand what is going on.

Liberty GT, 2010, 160k. Went to the dealership for one of the typical service, got the car back with strange symptoms - engine is shaking on idle on added load like AC compressor turning on or a transmission set to reverse.

With AC compressor, each time when it starts when engine is idling, there is a vibration wave for a couple of seconds. It is quite significant - can be physically sensed by hands on the steering wheel, via the driver chair etc.
The engine looks like choked for these couple of seconds and then comes back to a normal idle work. No such issue on rpm higher than idle.

With transmission put in reverse and the vehicle is kept stationary with brakes or with very slow moving backwards, it is just a high vibration.

I tried to return the car back to the dealership but they unable to actually fix the issue. They somehow increased idle by approx. 100 rpm, so the vibration become a bit less but the issue is still there. They mentioned an adaptation/relearn period after a battery disconnect but after a while the issue is still there. Plus I do not recall any previous battery disconnects did anything like that.

I looked through the internet and did the following but unfortunately that did not help:
a) gently cleaned the throttle - there was a bit of dirt there but not too much to worry about
b) did a throttle idle re-lean ( wait some time after turning ON but not starting the engine)
c) checked for diagnostic errors - nothing found
d) checked transmission oil level - OK

Apart from this vibration, the car drives as it was, no problems with acceleration, no strange sounds, does not look like it has any misfiring. Real time data from ELM327 dongle & Torque looks ok at the first glance.

The works the service did were as follows: change of the engine oil, engine plugs, transmission oil, diff oil.


If someone have an idea where to look next to diagnose the issue please, please let me know.

Thank you in advance and best regards,
ilib11

P.S. If you can recommend a good service in Brisbane for further regular servicing - that would be great too.

[Yowie]

P.S. If you can recommend a good service in Brisbane for further regular servicing - that would be great too.

John French Motors at Woolloongabba have looked after our two Subarus for years. The know their stuff & don't charge like wounded bulls.

[bigBADbenny]

Avcs is one very basic item to rule out via testing or diagnostics.
Your specialist should tick that off the list.

Ime, the fault can develop over time whilst not triggering a cel till the symptoms are pronounced.

Avcs Faq: viewtopic.php?f=6&t=36504

[ilib11]

Thank you, bigBADbenny - I'll look into AVCS, the Avcs Faq you did is very helpful.

I plan to test them first with a basic test, then probably remove and clean & check them manually to ensure they move freely.

In terms of buying a replacement - what is the usual place to buy them?

I saw many affordable genuine Subaru parts in US but many sites do not ship internationally.
This one seems to be shipping everywhere: https://www.tascaparts.com/oem-parts/subaru-control-valve-solenoid-10921aa140, has anyone used them?
Or rockauto is better https://www.rockauto.com/en/partsearch/?partnum=10921AA140 ?
Thanks a lot!

[bigBADbenny]

See the FSM & parts faq for local vendors eg BCW or usually for 2.5t avcs solenoids: partsouq

Oem parts are recommended over aftermarket items too, eg subaru branded, reputable vendor.

Note the avcs faq recommends diagnosis over random parts replacement aka parts cannon.

[bigBADbenny]

With transmission put in reverse and the vehicle is kept stationary with brakes or with very slow moving backwards, it is just a high vibration.

That’s a clue.
Iirc its something involving closed loop idle vs open loop reverse.

Iirc you can temporarily blind test the car by unplugging the a/f sensor to see how the symptoms differ.

Why not log basic obdii engine parameters available on Torque during the fault modes, post a cloud link to the log?

Even better, use Btssm or Romraider.

Is idle higher in reverse?

[ilib11]

Thank you for the suggestion, bigBADbenny.
I think Torque says it is closed loop O2 for both AC compressor on/off and transmission in reverse.

Will try to get tomorrow
- confirmation on idle in reverse, from memory I think it stays the same or gets a bit lower.
- what happened with unplugged a/f sensor
- some logs

[ilib11]

P.S. Would it be helpful to simply disconnect both AVCS solenoids and see if the issue persists?
Is that ok to run the engine with disconnected solenoids?

[bigBADbenny]

I’m not sure but pulling certain sensors will trigger limp mode.
Eg you might not be able to rev the car over 3k rpm etc.

Best used for temporary testing.

The avcs faq has a neutral rpm test to provoke the issue.

[ilib11]

Ok so I did some test on idle, adding and releasing load ( AC compressor on & off, Transmission selector to R and back to P)
The results are:
- Idle seems to be dropped a bit in added load, then returned to the expected value
- unplugging a/f sensor does not change the issue, the car behaves the same. It just resulted in adding an error code for a/f sensor faulty. I erased it after this test.
- Here are some pictures from RomRaider graphs. It seems to be AVCS /OCV does not change much ?
- RomRaider logs are available https://mega.nz/file/oToBCKAb#zEfjgYBWhiFCHoLN9cSKfnCcTsi2v6jl1qskaEI1pms.
The logs consists of 3 attempts to turn on/off AC compressor and 3 attempts of switching the Transmission selector ( in this case the engine shaking is longer than a couple sec for AC turning on)

I deeply appreciate your further advise....
Kind regads,
ilib11

[LibertyTragic]

Just a thought, but perhaps they borked the spark plug gaps in the service?

[ilib11]

I would need to get the spark plugs extracted to check that According to the invoice, they installed 22401AA761 which are the right ones...

[ilib11]

Looked a bit into the logs....
RPM: 588-1014. Sure 588 is too low

Absolutely no movement:
Exhaust OCV Current Left (mA):64
Exhaust OCV Current Right (mA):64
Exhaust OCV Duty Left (%):9.41
Exhaust OCV Duty Right (%)9.41
Intake OCV Duty Left (%)9.41
Intake OCV Duty Right (%)9.41
IAM (multiplier):0.6875

Very little movement:
A/F Sensor #1 (Lambda): 1.04-0.92
Exhaust VVT Advance Angle Left (degrees):0-2
Exhaust VVT Advance Angle Right (degrees):0-2
Intake VVT Advance Angle Right (degrees):0-1
Intake VVT Advance Angle Right (degrees):0-1

Strange movement (for me):
A/F Correction #1 (%)
A/F Learning #1 (%)

[Stifull]

We take all 5 of our subarus to Subievolution .. Russell and the boys do an awesome job.. My thoughts on your issue would be ..First thing to do is make sure the oil filler plug is on tight.. long story, but if that's loose it can cause issues.. Second, make sure the spark plug power pack things are on tight. I had one come loose on my GT not long after I bought it and the power pac (not sure if that's the right name) on cylinder 3 had come almost completely out and was only held in place because it was resting on the chassis.. I pushed it back into place and did up the bolt and it was instantly fixed. If they replaced the plugs then they may not have tightened it up properly ... https://www.subievolution.com.au/

[ilib11]

Thank you, Stifull - will check the coils tomorrow.
What was the problem with the oil filler plug?
A suction of an extra air through the oil filler -> engine block -> heads -> PCV -> intake as I suspect? In this case if I fully open the oil filler plug that should also make a difference. I am curious to try that!

And thanks for the service recommendation!
Regards, ilib11