[551602]

I found this interesting

The 3 Most Common Subaru FB25 Engine Problems - Reliability

Learn about Subaru FB25 2.5L flat-4 engine problems. FB25 reliability issues including oil consumpion, carbon build-up, and cam carrier seals.

tuningpro.co

''Possible symptoms of excess carbon build-up on the FB25D engine include:

• Engine misfires
• Stumbling / hesitant acceleration
• Rough idling
• Power / performance losses

As carbon deposits form they begin restricting air-flow into the cylinders. This can cause engine misfires, which then often lead to stumbling and rough idle. These symptoms usually begin once carbon build-up becomes pretty severe on the FB25 engine.

One of the biggest symptoms and concerns with carbon deposits is loss of power. It’s a really hard symptom to notice, though. Carbon build-up forms over the course of tens and tens of thousands of miles. As such, power loss is gradual rather than something you’ll notice immediately.''

While neither of us have the direct injection engine, I think its safe to assume that high mileage that have not had any carbon cleaning most likely have build up.

 

[mhackney]

Sorry for the delay - life! My daughter was visiting from Colorado and we're leaving for a week vacation on Sunday. I took today off to do some projects including the Forester.

Today I removed and cleaned the throttle body. All I can say is wow, I have never seen anything so dirty. I have not reinstalled it yet as I have a question below.

Here are the before and after photos."front side" refers to the side you can see when you remove the air box. "Back side" is the side you can see with the TB removed.

Front side before cleaning

Back Side Before Cleaning

Front Side After Cleaning

Back Side After Cleaning

NOTES:

The Backside before shows lots of greasy clumps of carbon deposits. It was everywhere. I really didn't have to do much other than use the TB cleaning fluid, let it soak and then wash it out. I used a toothbrush on the butterfly surfaces and edges. Does this greasy build up indicate anything in particular?

The big question I have is - with the butterfly in its closed position as show above, it doesn't seat all the way so there is a visible gap as you see in the photo. However, I can gently push the butterfly into the closed position. Is this an issue or does it close all the way when installed? Does the reset procedure actually adjust the closed position of the throttle body stepper and perhaps that could be part of the idle issue I'm chasing?

Anyway, I got the official upper engine cleaning tool (apparently the last one in the US!) and after I get a reply to the butterfly gap I'm ready to move on and install the TB and clean the upper engine.

Thanks!
Michael

BTW, I am following a very detailed video on using the tool and maintenance kit: MrSubaru1387 "Keep Your Subaru Running Like New! Subaru Engine Maintenance Kit"

 

[551602]

That was far worse than mine when I cleaned it a couple of years ago. I can imagine that the intake and valves are pretty dirty, and probably the egr as well.
The slight opening of the throttle plate looks normal to me, in fact you can see the same thing at the 5:20 or so mark in this Mr Subaru video

.
Good luck with the cleaning. I think you are on the right track to fixing it.

 

[mhackney]

A buddy came over to use my wood shop and I showed him the butterfly, he asserts that is normal and it looks like it is so I'm going to reinstall and see what happens. Thanks Quadrari10. I did replace the EGR. Other than the die on stopping issue, it seems to be running nicely, It had a new head gasket installed recently so maybe the intake and valves aren't horrific.

 

[551602]

That amount of carbon on the back end of the throttle body would indicate you have a fair bit of carbon build up to my mind. Don't forget to perform the idle relearn procedure after your cleaning.

 

[mhackney]

I'm claiming victory! Drove 10 miles after good warm up with 20 quick stops. Idle was rock solid and accelerator response was noticeably improved!

I'm going to do the top engine cleaning and fuel injectors and then do a relearn.

But wow, what a difference that made.

 

[TheCaddyMan99]

Sorry to revive an old thread, but what was the fix? did the carbon cleaning solve your idle issues? did you perform the idle relearn?

 

[asealll]

I'm claiming victory! Drove 10 miles after good warm up with 20 quick stops. Idle was rock solid and accelerator response was noticeably improved!

I'm going to do the top engine cleaning and fuel injectors and then do a relearn.

But wow, what a difference that made.

@mhackney any news? i have a 2011 manual doing exactly the same thing. thank you