Rough idle and intake valve carbon build-up. How is this possible?

droptop335 · 08-22-2011, 01:31 PM

OK, so I need some assistance here from the experts...or at least someone who knows more than I do about this:

While my car was at the dealer I mentioned that I have noticed that it has developed a rough idle and just some diminished performance in general. They said they would check for any codes and get back to me.

When I got my car back, they said that no codes were indicating a problem that could cause what I described, but they did say I have carbon build-up on the intake valves. I am not sure how they determined this. The SA asked what kind of gas I had been using, and I told her that I have put nothing in the car except Chevron or Shell since it was brand new (2007, 42k miles). This struck me as a ridiculous question as I will explain below. Then they said it would be $700+ to clean them. I said "thanks but no thanks" until I could do my own research.

So here is my dilemma:

The N54 engine is direct injection, which means that the intake valve sees no gas, only filtered air and recirculated crankcase gases. I have a hard time seeing how recirc gases could cause significant carbon. Maybe it can over time, but I'm not sold on that. I'd appreciate being educated here...
Even if the above were true, the carbon build-up would be on the BACK, NON-COMBUSTION SIDE of the valves, correct? How is it possible that this can cause rough idle or poor combustion? The build-up can't be so bad that it somehow disrupts the airflow into the combustion chamber...so what's the deal?

Am I getting a bunch of horseshit from the dealer? I know people have actually observed and cleaned carbon build-up from their valves, and claim that it improves the issue, only to say that the rough idle returns again within just a few hundred or so miles...so was it really the cause, or were they just imagining the improvement?

Finally, I hear that Seafoam may help here, but I'm not so sure that a few seconds of exposure to seafoam would be enough to dislodge these deposits that people claim take metal brushes to remove...

Anybody?

tibra1 · 08-22-2011, 01:36 PM

Its because its a direct injection engine that you will see carbon deposits on the intake valves as a result of the combustion process. When you have port injection the fuel passes over the valves and the detergents in the fuel clean or minimize carbon build up..

Do the intake valve cleaning, as this is the only way to remove the carbon buildup..no amount of fuel cleaners will help w this. My suggestion is to try and find and indy mechanic who has done it...it will be alot cheaper than what the stealership charges you

I personally do not like using seafoam..as any pieces of carbon that break lose will get sucked right into your engine

droptop335 · 08-22-2011, 01:40 PM

OK, but I still want to understand:
1. How it gets there in the first place
2, How it can possibly affect combustion

Jeff@TopGearSolutions · 08-22-2011, 01:42 PM

Carbon deposits are left behind during combustion.
It doesnt effect combustion itself it effects the air flow to the combustion chamber.

GeorgiaTech335coupe · 08-22-2011, 01:44 PM

These cars burn a lot of oil, so there is a lot of crankcase gases. Build up can cause valves to not move as freely as they should.

I would've asked the dealer to explain why the type of gas you used affects carbon buildup. IMO, they love to make false claims to charge you. Always a good idea to test their knowledge.

tibra1 · 08-22-2011, 01:45 PM

Quote:

Originally Posted by droptop335

OK, but I still want to understand:
1. How it gets there in the first place
2, How it can possibly affect combustion

How does it get there?..The combustion of gas is an inefficient combustion process which leaves behind soot and carbon..

The build up of carbon will cause improper air flow through the valves..and will rob you of power, cause rough idle, detonation etc etc.

This is a well documented issue with the n54 around the 50K miles mark..

ExpensiveTaste · 08-22-2011, 01:46 PM

Quote:

Originally Posted by droptop335

OK, but I still want to understand:
1. How it gets there in the first place
2, How it can possibly affect combustion

Oil from your positive crankcase ventilation system is recirculated into the intake manifold from the valve cover and is sucked into the engine via the intake stream. Any roughness on the intake side of the cylinder heads will create turbulence in the air and ruin the venturi affect that the engine relies on to be efficient.

droptop335 · 08-22-2011, 01:46 PM

Any chance this issue is being taken care of through a TSB and they're just not telling me?

droptop335 · 08-22-2011, 01:49 PM

Quote:

Originally Posted by ExpensiveTaste

Oil from your positive crankcase ventilation system is recirculated into the intake manifold from the valve cover and is sucked into the engine via the intake stream. Any roughness on the intake side of the cylinder heads will create turbulence in the air and ruin the venturi affect that the engine relies on to be efficient.

This makes sense to me, thanks. Seems there should be a way to scrub the oil from the gases before they get sucked into the intake stream. Is this what the oil catch can is used for?

tibra1 · 08-22-2011, 01:55 PM

Quote:

Originally Posted by droptop335

Any chance this issue is being taken care of through a TSB and they're just not telling me?

No

jkrig · 08-22-2011, 01:56 PM

Quote:

Originally Posted by droptop335

This makes sense to me, thanks. Seems there should be a way to scrub the oil from the gases before they get sucked into the intake stream. Is this what the oil catch can is used for?

Sorta, but a catch can alone won't cure the problem, (certainly doesn't hurt) the majority of the carbon is a just bi-product of the fuel burn in the combustion process

droptop335 · 08-22-2011, 02:08 PM

Quote:

Originally Posted by jkrig

Sorta, but a catch can alone won't cure the problem, (certainly doesn't hurt) the majority of the carbon is a just bi-product of the fuel burn in the combustion process

I didn't realize there was so much gas recirculation so as to cause this issue...maybe they shoulda teflon-coated the back side of the valves! LOL

droptop335 · 08-22-2011, 02:09 PM

Quote:

Originally Posted by tibra1

No

Of course not...silly me

secretsquirrel · 08-22-2011, 02:12 PM

Quote:

Originally Posted by droptop335

Any chance this issue is being taken care of through a TSB and they're just not telling me?

As Tibra said, no. Nasty valves is not a defect. Its just a bad characteristic of DI engines in general (at least high performance Euro engines). Other manufacturers are beginning to use DI engines (toyota/lexus and ford). I'm pretty sure there owners wont be as understanding about sludge issues as luxury Euro owners, so I would expect them to have a solution pretty quickly.

BMWsky · 08-22-2011, 02:29 PM

Quote:

Originally Posted by secretsquirrel

As Tibra said, no. Nasty valves is not a defect. Its just a bad characteristic of DI engines in general (at least high performance Euro engines). Other manufacturers are beginning to use DI engines (toyota/lexus and ford). I'm pretty sure there owners wont be as understanding about sludge issues as luxury Euro owners, so I would expect them to have a solution pretty quickly.

Add Nissan to that list. A friend of mine has a Nissan with a DI engine/turbo and guess what failed...the HPFP.

droptop335 · 08-22-2011, 02:39 PM

Quote:

Originally Posted by BMWsky

Add Nissan to that list. A friend of mine has a Nissan with a DI engine/turbo and guess what failed...the HPFP.

Which Nissan has a DI engine, GTR?

BMWsky · 08-22-2011, 02:42 PM

Quote:

Originally Posted by droptop335

Which Nissan has a DI engine, GTR?

My friend isn't that high end...she has a Juke.

droptop335 · 08-22-2011, 02:43 PM

Quote:

Originally Posted by BMWsky

My friend isn't that high end...she has a Juke.

Knew it was turbo...didn't know it was DI...

mithiral67 · 08-22-2011, 05:18 PM

search the forums, 2-3 decent write up on how to clean them at home.

Ozzie Goat · 08-22-2011, 05:50 PM

OR
Reading stumbling/jerky acceleration threads, pottypants (I think) suggested an olde school solution to this new age DI problem.
Took my car out on the open highway. 80mph 4th gear 30 minutes at about 4k.
Never visually inspected carbon on my valves, but the stumbling is gone.
It's free, try it.

mithiral67 · 08-22-2011, 06:01 PM

old school italian tune job?

Ozzie Goat · 08-22-2011, 06:05 PM

Yea. I know not everyone is as ancient as I am, but..
"Back on the day" Dads would take the Country Squire out on the weekends, hit the highway to blow the carbon out.
Always thought it was a wives tale, but it worked for me.

08-22-2011, 01:31 PM	#1
droptop335 Captain 39 Rep 709 Posts Drives: '07 335i (E93) Join Date: Apr 2007 Location: Back in SF Bay Area (Tri-Valley), WooHoo! iTrader: (1)	Rough idle and intake valve carbon build-up. How is this possible? OK, so I need some assistance here from the experts...or at least someone who knows more than I do about this: While my car was at the dealer I mentioned that I have noticed that it has developed a rough idle and just some diminished performance in general. They said they would check for any codes and get back to me. When I got my car back, they said that no codes were indicating a problem that could cause what I described, but they did say I have carbon build-up on the intake valves. I am not sure how they determined this. The SA asked what kind of gas I had been using, and I told her that I have put nothing in the car except Chevron or Shell since it was brand new (2007, 42k miles). This struck me as a ridiculous question as I will explain below. Then they said it would be $700+ to clean them. I said "thanks but no thanks" until I could do my own research. So here is my dilemma: The N54 engine is direct injection, which means that the intake valve sees no gas, only filtered air and recirculated crankcase gases. I have a hard time seeing how recirc gases could cause significant carbon. Maybe it can over time, but I'm not sold on that. I'd appreciate being educated here... Even if the above were true, the carbon build-up would be on the BACK, NON-COMBUSTION SIDE of the valves, correct? How is it possible that this can cause rough idle or poor combustion? The build-up can't be so bad that it somehow disrupts the airflow into the combustion chamber...so what's the deal? Am I getting a bunch of horseshit from the dealer? I know people have actually observed and cleaned carbon build-up from their valves, and claim that it improves the issue, only to say that the rough idle returns again within just a few hundred or so miles...so was it really the cause, or were they just imagining the improvement? Finally, I hear that Seafoam may help here, but I'm not so sure that a few seconds of exposure to seafoam would be enough to dislodge these deposits that people claim take metal brushes to remove... Anybody? __________________ Alpine White/Coral Red/Gray Poplar Convertible Sport/Prem/Step/Comfort/Nav/Sirius MHD Stage 1 Flash, M-Factory Helical LSD By the way people: USE YOUR F&*#ING TURN SIGNALS! Pass the word.
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08-22-2011, 01:36 PM	#2
tibra1 Banned 127 Rep 6,773 Posts Drives: 2011 ZCP M3 - 2007 335i crashd Join Date: Apr 2009 Location: NYC iTrader: (4)	Its because its a direct injection engine that you will see carbon deposits on the intake valves as a result of the combustion process. When you have port injection the fuel passes over the valves and the detergents in the fuel clean or minimize carbon build up.. Do the intake valve cleaning, as this is the only way to remove the carbon buildup..no amount of fuel cleaners will help w this. My suggestion is to try and find and indy mechanic who has done it...it will be alot cheaper than what the stealership charges you I personally do not like using seafoam..as any pieces of carbon that break lose will get sucked right into your engine
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08-22-2011, 01:40 PM	#3
droptop335 Captain 39 Rep 709 Posts Drives: '07 335i (E93) Join Date: Apr 2007 Location: Back in SF Bay Area (Tri-Valley), WooHoo! iTrader: (1)	OK, but I still want to understand: 1. How it gets there in the first place 2, How it can possibly affect combustion __________________ Alpine White/Coral Red/Gray Poplar Convertible Sport/Prem/Step/Comfort/Nav/Sirius MHD Stage 1 Flash, M-Factory Helical LSD By the way people: USE YOUR F&*#ING TURN SIGNALS! Pass the word.
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08-22-2011, 01:42 PM	#4
Jeff@TopGearSolutions 3441 Rep 79,211 Posts Drives: C6 Z06, 09 335i, 10 335xi Join Date: Dec 2008 Location: www.TopGearSolutions.com iTrader: (37)	Carbon deposits are left behind during combustion. It doesnt effect combustion itself it effects the air flow to the combustion chamber.
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08-22-2011, 01:44 PM	#5
GeorgiaTech335coupe Lieutenant Colonel 76 Rep 1,883 Posts Drives: Black BMW 335i coupe Join Date: Mar 2007 Location: USA iTrader: (0)	These cars burn a lot of oil, so there is a lot of crankcase gases. Build up can cause valves to not move as freely as they should. I would've asked the dealer to explain why the type of gas you used affects carbon buildup. IMO, they love to make false claims to charge you. Always a good idea to test their knowledge. __________________ Legal Disclaimer: Anything I or anyone else says about my vehicle on this website(e90post.com or any affiliated or nonaffiliated sites), pertaining to modifications, is only to gain acceptance from my/our peers, and does not actually represent anything actually existing on my car, and thus, cannot be held against me in any issues, i.e. warranty claims, that may arise.
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08-22-2011, 01:46 PM	#8
droptop335 Captain 39 Rep 709 Posts Drives: '07 335i (E93) Join Date: Apr 2007 Location: Back in SF Bay Area (Tri-Valley), WooHoo! iTrader: (1)	Any chance this issue is being taken care of through a TSB and they're just not telling me? __________________ Alpine White/Coral Red/Gray Poplar Convertible Sport/Prem/Step/Comfort/Nav/Sirius MHD Stage 1 Flash, M-Factory Helical LSD By the way people: USE YOUR F&*#ING TURN SIGNALS! Pass the word.
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08-22-2011, 05:18 PM	#19
mithiral67 That guy 117 Rep 5,740 Posts Drives: 2015 Cayman GTS Join Date: Jun 2008 Location: Chicago Burbs iTrader: (4) Garage List 2015 Porsche Cayman ... [0.00]	search the forums, 2-3 decent write up on how to clean them at home.
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08-22-2011, 05:50 PM	#20
Ozzie Goat Enlisted Member 0 Rep 40 Posts Drives: 2008 335i Convertible Join Date: Apr 2011 Location: Downers Grove, IL iTrader: (0)	OR Reading stumbling/jerky acceleration threads, pottypants (I think) suggested an olde school solution to this new age DI problem. Took my car out on the open highway. 80mph 4th gear 30 minutes at about 4k. Never visually inspected carbon on my valves, but the stumbling is gone. It's free, try it.
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08-22-2011, 06:01 PM	#21
mithiral67 That guy 117 Rep 5,740 Posts Drives: 2015 Cayman GTS Join Date: Jun 2008 Location: Chicago Burbs iTrader: (4) Garage List 2015 Porsche Cayman ... [0.00]	old school italian tune job?
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08-22-2011, 06:05 PM	#22
Ozzie Goat Enlisted Member 0 Rep 40 Posts Drives: 2008 335i Convertible Join Date: Apr 2011 Location: Downers Grove, IL iTrader: (0)	Yea. I know not everyone is as ancient as I am, but.. "Back on the day" Dads would take the Country Squire out on the weekends, hit the highway to blow the carbon out. Always thought it was a wives tale, but it worked for me.
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