Hello! I'm new to this Site,have a serious question!

I have a problem. I just bought a 1995 525i about 5 months ago. The car drives great,and I couldn't be happier. But now I have to get it smogged. It has failed twice,and the mech. Said it was due to having excessive carbon build up! So, I have purchased a can of Seafoam to do the job. Has anyone used this product before? Second....my new problem is when I accelerate from a stop, I get a vibration/knocking sound! But only at a start, after 20 mph or 200,000 rpm's it will stop and drive regular again. ANY INFO WOULD BE GREAT!

Please change your thread's title. It is useless. Please read the stickys at the top of these forums on suggestions on that.

I am not sold on seafoam removing carbon, and there is nothing there that would remove hard carbon buildup that I know of, but I agree that it is safe to use on the car. There are many youtube videos and websites with detailed writeups explaining how this is done. It would be far better for you to google this info directly.

Please do the stomp test and pull the error codes from your car to get some clues as to the knocking problem. Sounds like a backfire or a misfire and those can be delicate to track and solve. The sticky threads mentioned earlier will have information on how to conduct the stomp test, and since you have just purchased this E34, there are a whole bunch of things that you ought to consider if you intend to keep this car for the long term and especially if it is your daily driver. The stickys on maintenance would have the info that you need. Please take the time to read that carefully. Cheers.

knocking is probably the driveshafts center support bearing if it becomes a faster frequency with road speed increase, especially if louder under hard acceleration.