BCD-1

Carbon deposits on the intakes are a lesser problem with DI engines*. Deposits in this case are more a function of the emission control system.
I think they were taking a shot in the dark. What are your driving habits? I have a feeling that our engines are not made for city driving. Well, that goes without saying, but unless they can get good and hot at higher rpm's often enough they may be prone to carbon plaque. Not that that was your problem anyway.
Describe to me exactly how the misfire feels, when it occurs, how often it occurs, the load conditions, engine temperature, air temperature, etc. I assume you have no codes (there can be codes even with the CEL not coming on). Did BMW install an event recorder in your car and let you drive it for a while until the skip occurred? Probably not, they're not that sophisticated. The onboard data recorder may catch a glitch but unless you can identify a specific time frame it is difficult to sort it out of the data stream.
Have they identified the misbehaving cylinder(s)?

*There have been problems with carbon deposits inside the cylinders, on the piston crown and under the cylinder dome. BMW has blamed this mostly on the use of poor gasoline. However there are a couple TSBs addressing the carbon issue, one dealing with bad (leaky/poor spray pattern) injectors and the other with how to get rid of it. Your problem doesn't sound like it's related to this type of buildup because you don't mention 'ping' or rough cold start or other symptoms which go along with this type of buildup.

ELEVENS THIS I FOUND ON THE BMW Forums SITE
Look at the 1st question

Regards BCD-1

ELEVENS

I don't even know who you're talking, how it applies to the discussion, and to or what the "1st question" addresses. (BMW) "..is not that sophisticated." ??? Really?! I give up.

BCD-1

What are your driving habits? I have a feeling that our engines are not made for city driving. Well, that goes without saying, but unless they can get good and hot at higher rpm's often enough they may be prone to carbon plaque. Not that that was your problem anyway.


It's pretty Clear for Me !

BCD-1

kleinbus

With my Q5 (3.2) I towed about 2-2.5k lbs trailer 1100 miles on I70 from Kansas City to Salt Lake City and few week later same back and trip was done 2-4 times a year.

From day one and 3 years later with 70k miles on it, mostly 60-80 mph it had carbon issue so unless you have towed more, drove harder, this carbon testing through MMI is one of the greatest BS from dealer so far as Elevens already pointed out...

How many Beemers you actually have owned? With our previous 2 (328 and 335) our dealer in Los Angeles was far more sophisticated than our VAG dealer.

HaveBullDogWillTravel

What's Clear?

BCD-1

The test is done through a Vas Computer that plugs under the steering wheel. That communicates with the MMI.
It checks the Secondary valve injection
Complete carbon test , Misfires, injectors, complete injection system.
It takes around 45 minutes - 70 minutes for the Q to complete the test.
The test results are Negative or Positive.

I'm not a technical Mechanic like most of you Guys.
The Results on My Q5 were Negative 0.00 On The Vas Computer.

BCD-1

AudiQ5sleeper

all cars are bound to have carbon build up.

Poncherelly

My CEL came on so I had the dealer check it out. As with others, I have a carbon issue even though I only use top quality fuel and drive mostly highway. The light has now been on for two weeks while I wait for my appointment. This past weekend I pulled my travel trailer to the campsite with the family (since the dealer told me the issue will not affect anything). The camp Site is about 1:45 away and the Q5 handled perfect. We got home,etc on Monday and I filled up once again with the high grade fuel. While driving home from the gas station, I noticed my CEL is now off!? I'm still keeping my appointment with Audi, but thought it funny that this happened.

If anything further comes from this, I'll chime in further.

BCD-1

Poncherelly which fuel have you been using Petrocanada
ULTRA 94 ?

BCD-1

Poncherelly

Was using Shell but the last fill up I used petroleum 94. Didn't notice the light was off until after the fill up, but I doubt the short drive with 94 resolved the problem.

But hey, what do I know