Just purchased 1990 525i. It has (when purchased) an intermitent noise, lasting from 5 to 20 sec then off for 5 to 15 sec (this changes). Goes up and down with RPM. Apparently some connection to miles per gal hand in instruments (not the computer??) as hand drops about 5 mpg when noise comes and goes up the same when quite.
Could this be check valve or ??relay/? in the miles per gal. gauge system? Will get into car to try and find it this week end. 60+ year shad tree mech, firt BMW. Do 98% of own work.
ANY suggestions appreciated.