In my limited experience, if a quick pkug in with a code reader doesnt find any fault codes then look at the "dumb" components such as coil pack or MAF sensor.
The latter was failing on my 1.8 20v APK motor, random misfire and loss of power, would barely run then clear and go like a stabbed rat.
I was convinced that it was the coil pack, but while waiting from one to arrive from Lithuania or somewhere I found an online post about MAF causing misfire-like symptoms.
So I nicked the MAF off a known good 2000 Mk4 Golf 2.0 gti engine that has been hanging around and it cured it in one hit!
Not perfect, slight hesitation mid-range but driveable. Then I could source the correct MAF from the Bosch part number, I had the choice of mad money from Germany or a chinese knockoff from some Bulgarian on ebay...
The Bulgarian came good at £35 😄