Topic: Rough idle, boost surging at 3000rpms. 2006 Outback XT. **(Update 10 16 2017

[Victor]

Hello, I replaced the engine in my 06 Outback with a new short block, rebuilt heads, turbo etc. As it sits at the moment, there is no aftermarket add ons only a stock configuration. While driving at partial throttle, it has a surge at 3000rpms more like a gentle surge as though someone is on and off the throttle very quickly. Looking at the data on the scan tool, short term fuel trim is up to 22% and long term is at 14% and has triggered a P0171 Fuel system trim too lean Bank 1.

It has a rough idle, I don't feel as though it's a misfire though.

Checked fuel pressure

@idle 33-35psi
@3000rpms fuel pressure goes from 40-55psi.
@WOT fuel pressure stays steady 40psi.

Going with the code P0171 Fuel system trim too lean, it appears the engine is trying to compensate for the lean condition up to 21% Whichever threshold it has until it decides to trigger the light.

Any thoughts guys? It's an all stock EJ255, automatic.



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[Airboy]

Fuel pressure should rise fall with manifold pressure.  At 0psi boost, it should be ~45psi, at 10psi, it should be 55psi, etc.

[Victor]

Working off of the repair manual,

-33-38psi with the engine idling vacuum source plugged in. Test result 33-35psi @idle
-41-46psi with no vacuum source. Test result 40-55psi (throttle angle dependent, please refer to OP.

Should I be concerned of these numbers?

[toytech]

P0171 usually indicates a vacume leak , check to make sure all your lines are hooked up and that the intake gaskets are not pinched .

[Victor]

Just thought I'd give everyone an update on what we found, the culprit was the turbo inlet duct. It has tears and holes on the side of the pipe, thus letting in unmetered air into the engine. Replaced it with a new one and it idles nicely!

Cheers,

 Victor

[Victor]

UPDATE 10/16/17

After replacing the turbo inlet duct, the car would still have a rough idle. The rough idle would occur frequently, however DTC's are triggered rarely. When the DTC's did show, a P0301 and a P0172 would appear. Freeze frame data would show coolant temp to be registering a -40 degrees celsius! Replaced the coolant temperature sensor, now the car idles nicely! When the computer saw that momentary -40 degrees, it would dump all the fuel into the cylinders thinking it was trying to cold start in Antartica!

Hopefully this helps some of you out there that are experiencing this symptom! PM me for any questions!

Vic