P0303 Mazda -

Question

Replaced all 4 spark plugs and the car is now not stalling at idle and there is no hesitation when accelerating. The problem seems to have been fixed by replacing the spark plugs, but the check engine light is still on and the code P0303 is still being thrown.

Answer 1

try to swap the ignition coils, from cylinder 3 to cylinder 4 and clear the code if the code moves to the other cylinder than the ignition coil is bad.

If you still have the same problem a fuel injector might be clogged or bad. you can use 91 octane fuel and run a fuel system cleaner like BG 44k or 3M