I have the same car but in a sedan with the titanium package. I've never fueled with less than 91 but yes, the sensors should simply retard the timing on 87 octane fuel to prevent knocking. It doesn't strictly say in the manual that 91 octane is required, only "recommended".

I'm confused though, you said you had to add octane booster because the knocking was so bad? Doesn't sound like it was doing very well on 87.

I have been alternating back and forth between Ultra 94 @ Sonoco and Esso Supreme and oddly enough I'm getting at least 1L/100km better mileage on the Esso Supreme. I kind of have the feeling the ultra94 around here is ancient because nobody buys it, that or the local small stations (UPI) are just filling the underground tank with midgrade or regular. I find my engine runs noticeably better on Esso 91 which doesn't seem right to me.

 

To get somewhat back on subject ....... to clean carbon deposit the only sure way is to physically clean it. That means taking apart things and blasting, scraping and brushing away the carbon deposits.

 

Unfortunately I agree with you Mikeh. It's a bitch of a job. There are some fancy treatment solutions that certainly dealerships offer I forget what its called but I want to say "BG treatment" where they hook some canister up to line into the head and it sucks in some cleaning juice but its more of a preventative treatment. Once you have bad buildup, it's time to pull the head, or in my case with the 3.2: heads.

 

Lucky you have the 06' S4 mikeh... no direct injection for you.

 

True. The RS4 certainly has the problem as indicated by Stevelev

 

Yeah, apparently the RS4, R8 and 3.2's get the worst of it... Saw a pic somewhere of an R8 4.2 getting a turbo kit and it was just chaulk full of carbon.

 

Down here in the States we have a chemical additive called "SeaFoam". Works wonders on carboned-up valve stems and on the crap in the cylinder. Check their website at seafoamsales.com for exact instruction for each treatment method and go for it. Cut and paste this link.....eh! (Don't get your back up - I lived many years in Montreal!) (Eh!)

 

SeaFoam will do nothing for an FSI as it will make no contact with the valves or valve-stems, which is the reason why there is buildup in the first place.

 

Steve knows his stuff but you could try seafoam to loosen it up and then run it at 3 in the morning doing 210 on the highway..... It *may* work lol.... AND you have fun with the cops.