BMW's 22-year-old 3 Series b48 engine idles at 850 for a while and 700 for a while.

What you want to ask is what happened to BMW's 22-year-old 3-series b48 engine idling at 850 and 700? There is carbon deposition; Engine foot is aging and oil pressure is unstable.

The reasons for the uneven idle speed of BMW b48 combustion control are: engine carbon deposition; The engine foot is aging and the oil pressure is unstable. Serious carbon deposition in the engine: The common cause of automobile vibration is that the throttle valve is too dirty or the fuel injector has too much carbon deposition.

Idle speed refers to the state that the internal combustion engine keeps the lowest running speed. Usually in this state, the engine can provide enough energy for normal operation and use its auxiliary functions, such as pump, generator or power steering, but it can't do normal work, such as driving a car. Generally, the engine speed of passenger car is about 600 to 1000 rpm when it is idling.