Technical Car loses all power at high speed, have to restart engine

[Troughy]

Hey everyone, today while going around 130-140km/h my car suddenly lost all power (gas pedal didn't do anything) the check engine light started flashing and there was some rattling noise coming from under the car (maybe back/back right side). I pulled over and looked inside the engine bay and under the car just to make sure nothing was obviously broken, I didn't see anything out of the ordinary so I restarted the car and it worked fine. I did scan the codes with a cheap Aliexpress OBD scanner and two codes came up: P0300 and P0302, indicating a misfire. (I haven't scanned the codes since I bought the car a few months ago so they might have been there already)
Having bought this car used with over 214.000kms and no service history, I am planning on replacing the spark plugs, belts, water pump and fuel filter. I also think I might have a vacuum leak but the symptoms kinda went away so I didn't bother checking yet.
Interestingly enough, before buying this car I checked out a used Grande Punto, and the dealer said it had a problem where it loses power at around 130-140km/h but once you restart the engine it works fine. That was exactly why I didn't get that one, but turns out mine has it too.
This was the first time I went over 130km/h but I'm glad I did because I was planning on driving on the motorway this weekend and the car losing power there would've been dangerous.
How should I go about testing stuff to figure out what's wrong? I'm planning on buying tools and learning how to fix my car so any help is hugely appreciated.

 

[GrandePunto PL]

First step to successful DIY is doing the homework, research. Plenty of similar problems (threads), just read the forum, search.
You can be new to the brand Fiat (and fixing cars), but can NOT be "new" (and use it as an excuse) to the Internet in the year 2025.
You'll not go far if you're not self-reliant. Don't ask textbook questions (forum is not a Google, Bing, Copilot, ChatGPT, Wikipedia, whatever).

YouTube is full (overloaded) with a car diagnostics channels. Thousands of videos of why the car is misfiring and so on. All levels, from the amateur/hobbyist, grease monkey part changers, to the Pro level (using oscilloscope, exhaust gas analysis etc.). See how it's done.

Speaking of Forum. Most valuable content here is under GRANDE section. You DON'T have a "different model" (Evo/2012 is a "lifting" mostly). Most Evo/2012 owners think that way (wrong way), so they completely ignore/drop the "Grande" keyword while searching the web (they don't "search", but start new forum threads every time new problem pops out - don't be like that).
For example, forum Guides for Grande will apply to your Evo/2012 (example, timing belt guide for 1,2/1,4 8V is the same for 1,2 8V in Evo/2012, because it's an Euro5 standard, so 1,2 got the VVT too). You have 8V unit (check the valve clearance Guide). Guides have a Discussion section (read it too).

Little "spoiler" (there's more):
Valve "lash" + timing + VVT (oil delivery, wear and dirt inside) + ignition + fuel (pressure/flow), is related to the power loss around 130 km/h.

Get proper OBD2 interface (like ELM327 + Yellow adapter) and Fiat specific software (free, universal code readers are useless), FES, MES, AlfaOBD.

PS
As an exercise, find, where is the fuel filter in the simple petrol/gasoline engines... Exam question: can you really replace it?

 

[Troughy]

First step is doing the homework, research. Plenty of similar problems, just read the forum, search.
You can be new to the brand Fiat (and fixing cars), but can NOT be "new" (and use it as an excuse) to the Internet in the year 2025.
You'll not go far if you're not self-reliant. Don't ask textbook questions (forum is not a Google, Bing, Microsoft Copilot, ChatGPT, whatever).

YouTube is full (overloaded) with a car diagnostics channels. Thousands of videos of why the car is misfiring and so on.

Speaking of Forum. Most content here is under GRANDE section. You DON'T have a "different model" (Evo/2012 is a "lifting" mostly). Most Evo/2012 owners think that way (wrong way), so they completely ignore/drop the "Grande" keyword while searching the web.
For example, forum Guides for Grande will apply to your Evo/2012 (example, timing belt guide for 1,4 8V is the same for 1,2 8V in Evo/2012, because it's an Euro5 standard, so 1,2 got the VVT too). You have 8V unit (check the valve clearance Guide). Guides have a Discussion section (read it too).

Get proper OBD2 interface (like ELM327 + Yellow adapter) and Fiat specific software (free, universal code readers are useless), FES, MES, AlfaOBD.

PS
As an exercise, find, where is the fuel filter in the simple petrol/gasoline engines... Can you really replace it?

Thanks for your reply. For the past hour or so I've actually been reading your (among others) comments on the cam belt replacement post. Interesting stuff. Sadly no MES users (not on the map at least) in Hungary so I'll probably buy a license.
About the fuel filter, I've been watching too much ChrisFix haha.. Now I've read a few lines in the Haynes manual and it does say the fuel filter is an integral part of the pump assembly, so I guess I won't be replacing that. I've just now read that the check engine light flashing probably does indicate a misfire so the codes were probably right. I'm hoping that maybe changing the belt, spark plugs and doing a phonic reset (I read you don't like that but don't really understand why - or what someone could do instead) will fix this.