Help! Carbon build up with knocking sound every 3 months
I have a 2010 118i and got knock sound from the engine around every 3 months after the first oil change at 3500 km. I did it at 3500 km because the light showed the oil level was low.It's been 2 1/2 years now. When I heard the knock first time, I went back to the dealer and had a thorough check but found no problem at all. So they cleaned the cylinder and I thought that would be it.
But after that, I got the knock every three months and I need to go to the dealer for cylinder cleaning. They had done some complete check and sent the data back to Germany but found nothing wrong.
Any one got the same problem with 118i? Or any suggestion will be very appreciated!
p.s. The knock sound comes around 1600 rpm when I hit the acceleration very gentle. And everytime they did find carbon build up in engine. I am using highest quality gas (octan 98) here and with ok driving style.