Idiotic repairs cms21

I've been playing some cms21 and i wanted to ask if some repairs i've had are really as stupid as i think.

1- The engine is working fine, but it's choppy, car does not start.

How the f engine is working and choppy if it doesn't start?

2-Tapping sound from engine bay + the engine has no power.

I've been checking everything that could cause that tapping, took the whole engine apart, nothing, one part left. Until i removed air filter cover. How the f this falls under tapping sound from engine bay?

Second thing is the engine has no power. No engine because i've already removed it while searching for a different problem. Guess what the problematic part was. Yes, it was air filter base from the same car.

Again, im not a mechanic, but those things sound pretty stupid.