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Stumble/Shudder at idle and around 1500rpm

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Hi from Australia,

Longtime lurker/first time poster here.

I really hope someone can help me with this, The car has been to 6 different mechanics including Subaru Australia and no one seems to be able to resolve the issue.

The issue started shortly after 75000 kms and the car now has 82000. It's a 2004 AUDM Subaru Liberty GT MY05 2.0L Turbo Manual.

when the revs are kept at The issue is car shudders/stumbles at idle especially when warmed up and around 1500rpm the whole car shakes. Normal/on boost driving seems fine, the car pulls like a train.

I am very frustrated with it and at a point I want to actually get rid of it.

The mods on the car:

3" Dump Pipe

Xforce Catback

with Standard mufflers



So far This is what has been done on the car:

Front O2 sensor replaced (with an updated OEM one)

Rear O2 sensor replaced (with OEM one)

MAF Sensor replaced (with OEM one)

MAP Sensor replaced (with OEM one)

Injectors pulled out inspected/cleaned/flow tested and put back in the car

Intank Fuel Filter replaced

Spark Plugs replaced with Brand new ones

Coil Pack inspected and checked.

Air Filter replaced (with OEM one)

AVCS Solenoids Pulled out inspected / cleaned and put back in the car all 4 of them

Checked for Vacuum Leaks/Smoke Test done

Compression test done (All with in specs)

Regular Services done on time with Royal purple oil (5W-30) and only OEM parts used including upper Cylinder Cleaner

Timing belt with new tensioner and pulleys done (Dayco Kit)

Water pump replaced (After market)

Always used Shell v-power 98

No Check engine light no diagnostic errors on ECU

Learning view Screen shot can be found here:


Rom raider Logs can be found here:


Please help me!!!

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That is correct its happening when in neutral and idling as well as when revs are kept at around 1500rpm.


What would cause A/F to behave high like that?


It is a custom tune/reflash done in Sydney using open source tools.


I reattached the logs here hope it helps , let me know if you guys need me to log anything else .

Ras11m Logs .csv

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well, the computer is adding a bunch of fuel, so its seeing a very lean combustion. so either your under measuring air (vac leak or sensor problem), or you have some sort of fuel delivery problem.


Check the turbo inlet for holes as a possible source of vac leak, you're at the age where they tend to fail. Other possibilities might be the fuel pump, or the o-rings in the fuel pump assembly.

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