Help needed

Background story: I bought a 2004 Nissan Micra in October , 2004 reg 1.2 litre petrol with 56000 miles. Car was running perfectly and smooth
Passed MOT first try in March and about a week after the car broke down back from work and was pushed home, the car had been left without running for 4 days.

After use of carbon cleaner and cleaned out the throttle body the car fired up, we cleaned the throttle valve and when the car started acting up again a few days later we thought it was the throttle body so a aftermarket one from Amazon was fitted which did not solve the problem.

I have taken the car to three different mechanics now without any luck and they seem as confused as I am.
The fault codes are:

PO300- Random/Multiple cylinder misfire deteced
P1611- NATS malfunction
P1171- intake error

The car has also changed air intake and changed from supermarket petrol to BP premium.

The car is now back to its original throttle body and all fault codes cleared (currently no check engine light, but very occasionally flashes ie misfire) the car fired up immediately even after a few days without running, but the problem is very intermittent.

Yesterday the car was driven approximately 50 miles without any problems until I was cruising on the motorway after 35 miles at 60 mph and started loosing power and could barely maintain 40 mph with gas pedal fully depressed, I pulled over to the side, turned the car off and back on again after 20 seconds and the car ran fine all the way home.
The car also misfired for a brief 15-30 sec which did not return at the beginning of the journey.

Last mechanic suggested it could be supermarket fuel ? And that I should change the fuel filter.
The work done by last mechanic was resetting the throttle body and clearing codes which did not return when he test drove the car. First two mechanic did not do any work on the car.

I don’t mind working on the car, but at this point it seems more like guesswork and any related experience and soloutions would be highly appreciated!
 
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So the throttle body has been re-learned.
After changing to BP premium petrol the car has been fine for a while now..
The last problem was the car could be running fine for a while, then suddenly loose momentum and struggle to maintain 40 mph. A quick on and off would sort the problem out.
Could a new fuel filter help? I am considering a new fuel filter, oil filter and oil change as it wouldn't hurt.
 
I think that a disposable fuel filter is not OEM fitted to the K12 & that the only a gauze mesh is located inside the fuel tank with the fuel pump?

Cross check & verify this with the Haynes workshop manual.

However, such an old car, 2004, may have been retrofit modified by any of its previous owners & an air leak frothing the fuel is possible?
 
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