Subaru Outback Forums banner

1 - 15 of 15 Posts

·
Registered
Joined
·
3 Posts
Discussion Starter #1
New member here. This forum seems like a good place to ask a question, since I have found a number of posts about throttle body cleaning.

2017 Ouback Limited. Our second one, after we traded the 2013. Nice car, comfortable on the highway, and I like most of the new gadgets.

I have 2 problems that may be related. First of all, I have noticed that when it is really hot outside (we live in Florida) and we have the AC running, the idle speed drops down quite low, to the point that the car starts to shake. If I put the shifter into Neutral, it gets a little smoother, but is still pretty low.

The second problem involves the car hesitating and surging. My wife mostly drives the car (I drive my 2000 Ford Ranger), and she complains that it happens all the time. I tried to identify it better, and thought that it was a matter of the transmission hunting for the right gear.

I brought both of these issues to my nearest Subaru dealer (1 hour drive from my home). They tested the car and agreed that there was some hesitation, so they changed the programming of the transmission. My wife swears that the car is now worse. I can't tell the difference.

The dealer says that the AC issue is caused by "carbon" on the throttle body, and says that I should have a fuel system flush done to clean it all out ($200, payable by me) . The car is 2.5 years old, with 26K miles, mostly on I-95 between Florida and the Baltimore area. It has never been used in any sort of dirty or dusty environment, has had all the recommended maintenance done by the dealer, except for me changing the oil and filter at 24K miles, and rotating the tires. My wife remembers that the dealer showed us a dirty air filter about 8K miles ago, and we agreed to pay to have it changed.

I have read all the comments about a dirty throttle body/plate, and I don't understand how this could affect a car that is within its warranty, with only 26K miles. My truck is 19 years old, with 95K miles, and I think that I cleaned the throttle body about 5 years ago, when I changed the air filter.

I would love to hear what others have to say about this dirty throttle body issues. Where does "carbon" come from to contaminate a throttle body? The air flow comes from outside, thru a nice air filter. This cannot be the same issue as coking in a conventional carburator, which sits on top of the hot engine, and can cook residual fuel when the engine is turned off. The throttle body has no fuel pass thru it whatsoever. It only passes air (and maybe some crankcase gases?). If it has to be done, then why is it not covered by the warranty? There is no mention of this procedure in the maintenance book.

I know this is long for a first post, but I am quite confused about the dealer logic. I don't want to say that they just want to take some money from me, but I am starting to wonder.

All thoughts are welcome, and FYI, I am an engineer.

Ralph Caruso
 

·
Registered
2017 Outback Limited 2.5, Twilight Blue/Ivory, Eyesight. Also 1995 BMW 525i with 240,000 miles
Joined
·
2,174 Posts
I think there was an ecu update that addressed idle shake. This was separate from a TCU update. Perhaps more knowledgable people can help.
 

·
Registered
2019 Subaru Outback Touring 3.6R
Joined
·
177 Posts
The throttle body is part of the emissions system and covered under a different warranty than the rest of the car. Ask the dealer about that.
 

·
Premium Member
2016 Tungsten Outback 2.5l Premium w/ES, OP 14, PP #4
Joined
·
481 Posts
search using "tsb 11-181-18" see if any comments relate to your low idle issue. Typically using top tier gas (www.toptiergas.com) negates most throttle body cleaning and "need" for a fuel system flush.
 

·
Registered
2019 Subaru Outback Touring 3.6R
Joined
·
177 Posts
The throttle is part of the emissions system and covered under a different warranty than the rest of the car. Ask the dealer about that
 

·
Registered
2015 Outback 2.5i Limited, Ice Silver/Black
Joined
·
1,809 Posts
1. I think you're right about the "hunting". The CVT is not linear like a standard auto and more "squishy" (the rubber-band effect).

2. I think the ECU reprogramming would be best for possibly minimizing the shakes, but it is still a 4-banger without balance shafts so it will never be super smooth. If only there was a throttle speed screw, you could turn the idle up 100 RPM and you'd be great.

3. You can do a lot of DIY fuel system cleaning with a good tank injector cleaner like Chevron Techron or Gumout Regane. You can get MAF and TB aerosols to clean the appropriate systems, but at 26K I would not suspect that is the issue. And of course, change your own air filter. They are supposed to be good for 30K.
 

·
Registered
2016 Outback Premium 2.5 CVT w/EyeSight+SRVD
Joined
·
6,722 Posts
... it is still a 4-banger without balance shafts ...
A boxer 4 doesn't need balance shafts. The only inherent imbalance is a small rocking couple perpendicular to the cylinder plane, due to piston/connecting rod offset.
 

·
Registered
2015 Outback 2.5i Limited, Ice Silver/Black
Joined
·
1,809 Posts
A boxer 4 doesn't need balance shafts. The only inherent imbalance is a small rocking couple perpendicular to the cylinder plane, due to piston/connecting rod offset.
Interesting, thanks!

I found this enlightening.
 

·
Registered
(Australian spec) 2019 MY19 Outback 3.6R CVT.
Joined
·
285 Posts
The dealer says that the AC issue is caused by "carbon" on the throttle body, and says that I should have a fuel system flush done to clean it all out ($200, payable by me) . The car is 2.5 years old, with 26K miles, ...
IMO, a fuel system flush won't clean the throttle body. Ralph, it is quite easy to see if the throttle body is dirty, it takes about 5 minutes to check with basic tools & a mirror. It shouldn’t be dirty on a Subaru naturally aspirated engine at your mileage (if it was the FA20DIT engine in the SJ Forester XT then that would be a different matter), but there could be carbon build-up in the combustion chamber. I checked the throttle body on our previous 2016 Liberty (Legacy) 3.6R at about 3 years & 36,000km & it was spotless. But if your throttle body isn’t clean, it is very easy to clean.

A few things to consider:

According to Subaru, overfilling engine oil will cause CVT surging. There is a topic somewhere on this forum about that with an attached TechTIPS document.

The MAF sensor may need cleaning with a MAF sensor spray cleaner (obviously don’t touch the sensor). I have had rough idling on a Subaru & a contaminated MAF sensor was the cause after the engine air filter was replaced.

In Australia we have two Subaru products that are required to be used at every service as part of the service (listed in the maintenance schedule). One is an upper engine cleaner (SA459) that gets sprayed into a vacuum line at every service & into the throttle body at about every 2nd or 3rd service, & the other is a fuel additive (SA718) that gets added to a full tank of fuel at each service (this is mainly for the fuel injectors I believe).

In my experience the upper engine cleaner definitely works on every Subaru I’ve owned or serviced, but in the case of the FA20DIT SJ Foz XT engine it wasn’t enough to keep the engine running smoothly at idle. Another Australian SJ Foz XT owner sourced a stronger product; Liqui-Moly Petrol Engine Intake Decarb, & this clearly worked on that engine. With both the Liqui-Moly & the SA459, the amount sprayed into the vacuum line or throttle body must be limited to prevent the risk of hydraulic lockup.

I can post more on the upper engine cleaner if required.
 

·
Registered
Joined
·
3 Posts
Discussion Starter #11
IMO, a fuel system flush won't clean the throttle body. Ralph, it is quite easy to see if the throttle body is dirty, it takes about 5 minutes to check with basic tools & a mirror. It shouldn’t be dirty on a Subaru naturally aspirated engine at your mileage (if it was the FA20DIT engine in the SJ Forester XT then that would be a different matter), but there could be carbon build-up in the combustion chamber. I checked the throttle body on our previous 2016 Liberty (Legacy) 3.6R at about 3 years & 36,000km & it was spotless. But if your throttle body isn’t clean, it is very easy to clean.

A few things to consider:

According to Subaru, overfilling engine oil will cause CVT surging. There is a topic somewhere on this forum about that with an attached TechTIPS document.

The MAF sensor may need cleaning with a MAF sensor spray cleaner (obviously don’t touch the sensor). I have had rough idling on a Subaru & a contaminated MAF sensor was the cause after the engine air filter was replaced.

In Australia we have two Subaru products that are required to be used at every service as part of the service (listed in the maintenance schedule). One is an upper engine cleaner (SA459) that gets sprayed into a vacuum line at every service & into the throttle body at about every 2nd or 3rd service, & the other is a fuel additive (SA718) that gets added to a full tank of fuel at each service (this is mainly for the fuel injectors I believe).

In my experience the upper engine cleaner definitely works on every Subaru I’ve owned or serviced, but in the case of the FA20DIT SJ Foz XT engine it wasn’t enough to keep the engine running smoothly at idle. Another Australian SJ Foz XT owner sourced a stronger product; Liqui-Moly Petrol Engine Intake Decarb, & this clearly worked on that engine. With both the Liqui-Moly & the SA459, the amount sprayed into the vacuum line or throttle body must be limited to prevent the risk of hydraulic lockup.

I can post more on the upper engine cleaner if required.
Thanks to all for your suggestions. I think I will try out a fuel cleaner first, and also take a look at the inside of the throttle body when my wife gets back with the car and it cools down. Unfortunately, we are in the rainy season here in Florida, and my garage is full of boat stuff, so I don't know when I will get to it.

@XT0sub - this is really useful. I did not understand how the throttle body could be contaminated with carbon, or be cleaned by a fuel system flush, either. Makes no sense. Fuel never .goes thru it. And the idle issue only occurs when the AC is running, and it is HOT outside. If I turn off the AC while at a light, the idle comes back up to a normal speed, and it is nice and smooth.

The comment about the emission warranty is something I did not think of. They have a much longer warranty, and I have done all the required maintenance, so I think I may have to insist that Subaru deal with this on their own dime.

I will let y'all know what happens.
 

·
Registered
2015 Outback 2.5i Limited, Ice Silver/Black
Joined
·
1,809 Posts
When you replace the rubber intake connector to the TB, make sure it is connected all around. The collar is pretty soft and easy to have roll up on the bottom side of the TB.
 

·
Registered
Joined
·
3 Posts
Discussion Starter #13
FYI about the dirty throttle body/fuel system. I called Subaru and explained the situation to them. The fellow I talked to was very quick to make an offer to pay for this service. He sent me a coupon that covered the cost, and I just had the work done by the dealer today - "Premium Fuel Induction Service" - $189 + tax. The car seems to run a bit more smoothly than before. I don't know whether it solves the shifting problem - my wife is more sensitive to that than I am, so she will have to take it out and see how it handles.

The dealer gave me a brochure for the cleaning service, from a company named BG Products. It was explained that they put a can of cleaner into the tank, and use a special machine to spray clean the throttle body and the intake manifold. Supposedly, new engine technologies such as variable valve timing, gasoline direct injection, and low tension piston rings are the culprits, because they allow exhaust gases to leak back into the inlet manifold. This sounds like something that the Manufacturer should be dealing with, and I would be tempted to report it to the EPA, because it affects emissions. The brochure has photos of the insides of high performance German cars that have significant deposits with less than 30K miles.

I will see how it works, and then get back to Subaru about this. I have a 30K service coming up, which includes "checking" various fluids, including the CVT. On my last Subaru at this point, they told me that I needed a CVT flush, because the fluid was dirty. A bit of reading seems to indicate that Subaru does not like anyone to flush CVTs, or take them apart, because they like to look at the insides to figure out why the fluids are dirty - they are supposedly guaranteed for 100K miles. No idea how much of this is true or BS - I could not find anything official from Subaru about it. Dealers charge about $700 to do a flush (I know), and it seems to be a very special event. Not something like changing engine oil.

More to come.
 

·
Registered
2017 Outback Limited 2.5, Twilight Blue/Ivory, Eyesight. Also 1995 BMW 525i with 240,000 miles
Joined
·
2,174 Posts
BG product are well-respected products. BTW, the general rule is do not power flush any automatic transmission. just drain refill. $700 to service transmission is outlandish.
 
1 - 15 of 15 Posts
Top