The throttle of the old Mazda 3 is rotten.

Idle speed instability caused by improper idle speed adjustment, dirty throttle body and poor idle speed control system.

Touch the ignition coil by hand. If it is overheated, the ignition coil has been damaged and should be replaced. Check whether there is a high-voltage fire in the central high-voltage line. If there is no fire, the low voltage circuit is short-circuited. Check whether the ignition head leaks electricity. Check the distributor,

Check whether the signal induction coil in the distributor is burnt out. If so, the signal induction coil is damaged. Start the engine and see if the ignition head rotates. If it cannot rotate, the timing drive belt teeth are damaged and should be replaced.