It appears the intake valves are carboning up bad. My guess is with no gas contacting them perhaps they are running a lot hotter. Anyways service bulletins have been sent out to various makes dealers. Apparently the manufacturers have been trying to keep it as quiet as possible.

Symptoms are poor idle and running. Cure is removal of the carbon. I wonder if periodic water injection might work? A small nozzle hole into the intake not disturbing the map sensor might work.

Bmw is using walnut shells somehow. Kia does not disclose their cure but recommends a good gas with a cleaning agent and additives to the gas basically on a permanent basis. The real cure apparently is too get a little of the injected spray to hit the intake valve. Probably a head redesign.

I think direct injection is here to stay on gas engines. The best guess is that the manufacturer can increase fuel milage by fifteen percent with higher low end torque. Or can choose instead to boost overall power using the same amount of gas.

I spent the day at a training class for the MB direct injection engines. Seemingly the Benz motors are not plagued with carbon build up like most other makes. While not a concrete explanation the instructor speculated its due to Mercedes having better crankcase ventilation execution than the lesser brands.

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90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197° intake cam w/20° advancer
Tuned CIS ECU
4° ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff

When I worked on 300SL's, the only two ways to keep a W198 engine running well were to rebuild it, or drive it hard!

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[GONE] - 1995 Mercedes E300 Diesel - 130k miles - Smoke Silver (702) over Mushroom leather (265) - Bladder blasting, coast-to-coast work machine.

I've got an 08 Mini (base) coming in in a couple weeks to look into this exact issue. Car has about 160k miles on it and is somewhat rough during cold start in addition to always having some type of cam related code. Considering picking up a walnut shell blaster which looks like what is necessary to clean it up.

Here is a link showing process on a BMW:

walnut shell blasting

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Jim

The BMW issue is decades old, back then DI didn't exist on those cars. BMW had Chevron develop or at least endorsed Techron as a fix for this. However Techron won't work on DI motors.

Some things I've seen on gas engines:

Engines with small camshaft events have less / non existant blackening of the intake ports. ( 301 Pontiac for example ) Engines with early intake opening / lots of intake to exhaust overlap do get blackened.

Non EGR diesels that don't connect the crankcase breather to the intake remain spotless.

I'd consider intake decarboning a maint item and not a failure of the design.

Common problem and walnut blasting is the common fix

Like TheDon said, pretty common on DI cars though it seems some are worse than others. Generally I just drive my cars hard which all of my DI engines seem to love and Iv'e never had a problem with carbon buildup. A nice ITU clears out quite a bit. I don't think its a necessarily unknown or big problem though.

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth

I doubt an additive would do much, the cleaner is going where the fuel is going, which isn't on to the back of the valve.

My girlfriend has an Audi 2.0T and so does my friends wife, we occasionally go out and drive them really hard, and you can get them to smoke noticeably the first couple pulls at WOT then it doesn't do it anymore. Haven't had any issues with check engine lights for misfires or other codes often associated with carbon buildup.

Like Duxthe1 pointed out, you almost never hear about Mercedes DI cars having issues which I've always found interesting. I appreciate him shedding some light on it, I like the crankcase ventilation theory. BMW air/oil separators fail pretty regularly and cause all kinds of issues so I could see it being at least partially related to that. This also is nothing new, DI has been in Audis since like '05, and BMW had carbon issues before it was en-vogue to have carbon issues . I wouldn't be too worried about it, its just sort of the way it is. Having to pull and walnut blast or manually clean the intake every 60-100k is not all that unreasonable in my opinion either.

I subscribe to tbomachines method of repair, the occasional full throttle blast on a merge whenever its safe to do so will help keep the buildup down.

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68 280SL - 70 280SL - 70 300SEL 3.5 - 72 350SL - 72 280SEL 4.5 - 72 220 - 72 220D - 73 450SL - 84 230GE - 87 200TD - 90 190E 2.0 - 03 G500

Nissan GTR - Nissan Skyline GTS25T - Toyota GTFour - Rover Mini - Toyota Land Cruiser HJ60 - Cadillac Eldorado - BMW E30 - BMW 135i

I have experienced this problem in a late 90s mitsubishi. (not in USA) - its problem was two fold.

firstly because of being a dry manifold and an EGR valve the size of a 1.5 inch pipe fitting it recycled exhaust like it was going out of style, The exhaust was soot loaded already because the engine was high CR. So we have a nice diesel black soot floating in the intake manifold.

add a bit of oily vapor in there (PCV) and you get a a nasty amalgamation of tar built up on the intake valves.

the part 2 of this problem was the carboning up of the crescent on the piston top which was necessary to tumble the mixture and keep it in place as the injector loaded fuel into it and the plug then fired it. - No tumble = no power cycle event = misfire = checklight.

Great when working - turbodiesel like torque - but a royal PITA to service, walnut shell blasting etc. some people used the GM piston cleaner to flood the engine and hope for the best as it washed the valves too as it went past.

The fuel pressure was nice too - 1800 or 2200 psi (if I recall correctly)

Toyota I believe have employed 2 sets of injectors in their lexus engines to keep this problem away - one firing in the manifold and one firing in the combustion chamber..

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

Toyota/Lexus have a simple solution for this. 2 sets of injectors both port and direct. Port injectors are used for cold start and WOT. That gasoline is enough to clean the backs of the valves. Everybody else has to get cleaned with walnut shells.

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CENSORED due to not family friendly words

https://www.youtube.com/watch?v=y4UhOeYYXAA

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Nate Stanley
(Currently Benzless)
1985 F-250 6.9l 170K
2009 SCION XB 36.5K
2003 LS430 78K
2012 Kubota B 2320

BMW has had a long standing history not only with poor crankcase ventilation but notorious for early failure of the valve seals. So not only are they breathing oily mist through the intake but plenty of oil runs down through the valve guides. I was a BMW factory trained technician for about 10yrs (hence I drive Mercedes!) before switching to airplanes. BMW used to build really good cars, I think that ended in the early 90's. Mini's are utter junk too, built by BMW of course.

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87' 300D, Currently undergoing an OM606 swap/build! SUPERTURBO!!!
03' 2500HD Dmax + goodies!
82' 300SD, parting out!
93' 300TE 4matic, parting out!
83' 240D Project Cheap Drive
89' 300E, parting out!
74' Datsun 510 wagon
88' RX7 10thAE, 13B track car build soon

Skippy~ As for perception: Drive what you like and can afford. Those who don't like it can supply vacuum to one of your components. LOL

If you need parts, I have some!

The only thing good I have to say about the Mini is that it is fun to drive.

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Jim

There are only so many new "Mini" variations one can make. The first new one, clubman, convertible, low roof ( whatever they are calling it ) I'm waiting for a reissue of the Mini Moke.

That reminded me of that old British TV series, "The Prisoner":