Please do these things and report back to us.

Change fuel filter.
Fix your code 07. You mentioned you wanna test your boost sensor. Test your WIRES. Your car is literally telling you what to fix and you haven't fixed it.
Is your BAC valve connector OVAL? Still waiting on this info.
Measure resistance of old and new injectors as suggested by FührerTüner. So YES, this means your UIM has to come off. You might actually have to do some work to get this resolved.

These are things you must to do. Do ALL of the above and post results... like, actual results. It should look something like this:

"I changed the fuel filter.
I fixed the code 07.
The BAC valve connect IS or ISN'T OVAL.
I measured the resistance of the old and new injectors and I measure X ohms."

EDIT: Save the UIM removal for last and test after fuel filter change and code fix. If it were me I would take it off just to get rid off those ebay parts.

 

Guys you are right, but I really have no time lately to actually troubleshoot the problem. But I will and I will post the results.

Meanwhile...I have been reading some topics in here and I was wondering If the thermovalve that is mentioned in this topic (https://www.rx7club.com/2nd-generati...tivate-405754/) can be responsible for my problem.

Also I read somewhere that the AFM should be horizontal. Why is that? Can this cause any troubles?

Thanks again for your patience and please forgive my laziness and lack of time.

 

No.

Some of these things take as much time and effort as you spend perusing this forum, such as just answering the question regarding your BAC connector.

 

Ok, so I am really busy lately and I can't visit the mechanic in order to check for the things that you have mentioned but I managed to take some photos of the engine bay.

I will post the BAC valve connector, the oxygen sensor connector, some other connectors that I don't know if they are connected properly after the UIM removal and to other points that you might find something wrong.

 

The BAC valve connector

The oxygen sensor connector

connectors next to TPS

non horizontal AFM...is this a problem?

intake

vaccum hoses. I found this plugged hose with a screw...is this ok?

 

Good news!!!
I finally managed to troubleshoot and solve the problem. I bought a multimeter and a pressure test kit and started to measure various sensors such as the boost sensor, air intake temp sensor etc.
The first problem was with the AFM built in temperature sensor. Luckily I had an old spare AFM so I replaced it. The second problem was with the TPS. The narrow range values where off range (1.26 Kohms while the normal range is 0.8-1.2).
So I used the tuning screw and set it to 1 Kohms. Now the car runs great.

Thank you all for your answers.