Question I have a 03 500I it has run great up to now. I have about 1400 miles on it Problem is it runs good at low speeds but when I get on it around 30 MPH + it starts to lose power and sometimes backfires. I have change the plugs and airfilter but does the same thing has anyone had this problem or no what may fix it.

Thanks.....Bob

 

maybe your belt is worn. But that would not cause backfire's.

 

Did you change the exhaust any? Backfiring is a lean symptom.

 

Either an exhaust change or dirt in the carb causing a partially blocked jet causing the lean condition.

 

Everything is standard nothing added. I change the plug and clean the filter still same problem. I will be taking it to the dealer tomorrow to have the valves/timing adjusted. I will post results when I get it back.

 

chances are i would agree with bear sounds like just a simple carb cleaning would do the trick. they are very easy to clean but if you are unsure i would find someone that is or take it to the dealership.