Is the idling instability caused by carbon deposition on the throttle or damage to the ignition coil?

If the ignition coil is broken, the engine will not start and the idle speed will be unstable for several reasons. First, the insulation degree of individual spark plugs decreases, which leads to the weakening of sparks. Second, the idle throttle hole is blocked, which makes the mixture too rich. Third, the high-voltage line is partially short-circuited or the insulation layer is aging and leaking. If several problems cannot be solved, it is necessary to measure the pressure of the cylinder.