you can clean the AFM by spraying it with carb cleaner, my mate bought a P11 that would barely tick over and wouldnt drive for cheap and I went over to help him faff about with it as the previous owner had changed almost everything from knock sensors to new dizzy and alternators. I checked the afm and it looked grey instead of shiny, quick squirt and the car was fine.
Also check tps, the earth on the afm, breather/vaccum pipes are clean/fitted properly.
And not but not least, whats the garage like where you went? They could be trying it on.