Volvo V40 1.6 l. 84 kW reduced engine power issues

[Memevoki]

Dear all,

I've been having issues with my Volvo V40 1,6l 84kW (year 2013) car. I am a new car owner, so I don't have much knowledge about cars or their parts. So this is what I experienced and was told by the mechanics.

To start of from the beginning, I bought the car around 4 months ago, everything seemed fine, all check ups went without a hitch. I decided to give the car to the mechanics to change the oil and filters related to it. After getting that changed, I fulled up the car with diesel as well. The next day, the car did not start... After leaving it and coming back from work, it started just fine. The next day I started driving to work and suddenly a turtle icon (reduced engine power) flashed up, then the car popped up a DSTC temporarily off message, the car reduced the speed and came to a halt, engine powered off. After turning the power off and on again, it went back to normal, until I was driving home, same thing happened. This started to happen a lot for a while, sometimes the car would try to start the engine without me doing anything, but it wouldn't start back up until I turned the power off and on again.

We took it to another mechanic to check the faults, they came up with nothing major, so they just deleted them. The car was fine after this, but then it did the same thing, but without popping up any warning this time, the engine just shut off several times in one go, it was trying to start, but it was more like it was coughing and not starting. After sitting for 10 minutes while off, it started fine again and was fine for around 3 weeks. We decided to get it checked just in case at another mechanic, they found that the car had major fuel pressure jumps at some points (one of these jumps happened when the engine was not even running). They suggested changing the fuel pressure sensor. But we are yet to do this.

A few days ago we took the car to get the engine belt changed and we also changed the air pump system (it is customary to change them at the same time, so why not). Today, when getting out of work, the turtle icon (reduced engine power) popped up, seemed like the turbo of the car was not working (stepping on the gas pedal did not show the usual results of speeding up). I stopped on the side of the road and re-powered the car. It fixed the issue. After some time it popped up again, did the same, all good. After driving around for a bit I started heading home and the engine started powering off again (no DSTC warning, but the turtle showed up before it started doing this). I noticed that the engine powers off a little while after pressing the clutch down and reducing the speed in neutral gear. It powered off like 6 times when I had to come to a near stop in roundabouts and crossroads.
After getting home and letting the car sit for a bit, I took it to test if it runs fine or not, it was fine until the same turtle popped up and it led to the engine stalling again when going neutral and pressing the clutch. After revving the car for a bit, the issue solved itself for 15 minutes I spent driving around and got home. No idea if it will suddenly pop up again tomorrow.

Does anyone have any ideas what could be causing these issues? I've read a lot of information in different forums. Some claim that this is the fuel pressure sensor, others claim it to be oil filters, fuel filters, bad fuel quality... I will try taking the car to get another checkup and change the fuel pressure sensor if they have one.