the car was evrywhere already i would think that they
checked the "easy" things already.
In my experience you would be WRONG, WRONG and then WRONG again to assume that.
In my Experience they would have replaced parts WITHOUT TESTING or CHECKING.
Forget that it has been to 6 other shops. Deal with what you have in front of you right now, start at the beginning with a robust, methodical test plan and assume nothing !!!
Start with the Fuel filler cap and slowly move forwards, inch by inch to the front of the car
Terbo, my friend !!
You have been advised at least twice, with good reason, not only by me, to confirm the Low Pressure Fuel Delivery Circuit FIRST ?
Could it be a injector or the security Valve at all in your opion ?
Yes !!! but you CANNOT rely on any test results at those components with an UNconfirmed LOW PRESSURE DELIVERY to the HP PUMP. BASICS FIRST !!!
Imagine yourself going to hospital thinking you are having a heart attack and the doctor is more interested in the bruise on your knee from playing football because it is easier, quicker and cheaper to test and fix ??? Don't be that doctor !!!