How do I try peugeot coil 307 2002 gasoline 2.0i

You should start by performing simple tests like the one I did (changing the injectors). I had a similar problem with a Nissan Quest, and it was the spark plug wires. In your case, it could be the spark plug jumpers or connectors.

Sometimes the spark plugs themselves fail; try cleaning and regapping them. If you can't buy new ones, try swapping them to see the effect of the test.

You could also use a scanner to check for any problems in the sensor history, as it could also be an intermittent sensor failure, since these can advance or retard the timing.

I'm not an expert, but I hope this helps a little. Good luck!

Thanks for replying, we actually thought the same thing. I swapped the injector positions, changed the spark plugs for new ones, and managed to get a used ignition coil. I installed it, and this time cylinders 2 and 3 worked, so I asked them to replace it with another one.
The one they sent also had the same problem, which I found strange, so I tried another coil from a 2002 Hyundai Accent. I wired it up, and it tried to start on the first attempt, but then it just backfired. After that, I installed the coil I bought, and like magic, it started smoothly. As for the scanner, it gave me several readings: knock sensor, air sensor, oxygen sensor, misfire in cylinders 1 and 2, misfire in cylinder 4, and catalytic converter malfunction.
I didn't replace any of the sensors because they tested fine.
Finally, when it started up smoothly, I scanned it again and cleared all the fault codes, and it hasn't shown any codes since. It's been three days now and it hasn't been malfunctioning at all. I hope it doesn't give me any more problems. Thanks a million to everyone.

Original coil or Chinese one? The Chinese one is crap. For all vehicles, you have to be careful; that coil is just one, but internally it works like two. If it's only those two cylinders, you can rule out a sensor problem because all four would show the same issue. If it's only those two, then it's definitely a coil problem because the spark is very weak and it's not burning the mixture properly.