When I turn the steering wheel, my Mazda 323 will shake and the tachometer will drop. What happened?

Because the power steering signal will affect the speed. So there may be two reasons:

1, your car's oil circuit, throttle and other oil and gas enter the stolen part, and the load increases when you hit the direction, so the phenomenon you mentioned will appear.

2. The cause of the steering system. It mainly includes: booster oil fault and the increase of resistance of booster system components caused by booster oil fault. Because the resistance increases, the load will definitely increase. What you said will happen again.