loss of power on Audi 100

I have an Audi 100 2.0E 1994 which is OK when started from cold and runs well. But after a few miles, if I stop and switch off the engine, when I return to the car after anything up to 3 hours later, although it starts well enough, when I pull away it loses all power within about 100 yds. It doesn't stall and if I push the clutch in and 'coax' the accelerator, it picks up and then drives ok again. The whole episode lasts around 30 secs max. A sensor problem? Any answers? thanks