The engine is a 1.0 TSI (3 cylinder) from VW, 2022 model year, 110 hp, manual, 100 000 miles.

The car initially suffered a high-pressure fuel pump (HPFP) failure, where metal shrapnel was released, which led to a complete fuel system replacement (HPFP, LPFP, all injectors, fuel lines flushed, fuel tank drained and cleaned, etc.), all done in the dealership, covered by (extended) warranty.

After collecting the car from the workshop, I quickly noticed hesitation/jerking during acceleration, mainly between 2,000–3,000 rpm, followed by a flashing check engine light and a stored misfire code on cylinder 1 (P0301). The car was returned to the workshop the next day, where they found a cracked EVAP hose, which was then replaced.

After that repair, the same symptom remained but became less frequent. The car generally drives OK, but intermittent hesitation/jerking still occurs, most often between 2.2–2.8k rpm and around 70-80% throttle. In the first few days, the issue could be deliberately provoked with stronger throttle input and would sometimes trigger a flashing CEL and the same P0301 fault. Now, almost 2000 miles later, the symptom still occurs occasionally, but it can no longer be reliably provoked and no fault codes are stored in the ECU, even when the hesitation happens. Long term fuel trim is 0% and lambda is 0.99

The issue tends to appear under conditions the car was not previously adapted to, for example when driving with more passengers or heavier load compared to driving alone. It may be slightly more noticeable when the engine is cold, but not dramatically. On the highway in 5th and 6th gear, the hesitation seems to occur more often than in city driving.

My concern is how this can now be properly diagnosed, given that the issue is intermittent, difficult to reproduce, and leaves no fault codes, and I am worried the workshop may start disassembling components without clear direction, potentially creating additional issues. Any insights or similar experiences would be greatly appreciated.