09Lancer randomly starts only after 3rd try and sometimes sluggish power

I drive a '09 Mitsubishi Lancer EX 1.5(A) unmodified. Engine is 4A91. At random times, the car would crank normally but doesn't start. However, it starts normally after 3rd try, and there is no engine check light. I rev the engine to about 3.5k RPM, and heard a soft backfire sound from the exhaust. Using a code reader, nothing was registered.

Generally, after this incident, the car would feel sluggish (includes gear shifts) or weak during acceleration and would recover in a day or two. There was also once when I had to step hard on the brake to stop normally. So, kindda suspect the vacuum lines and components like EGR and PCV valves.

What should I do?