2000 Vauxhall Corsa

The car starts, then the revs immediately drop to the point where the engine cuts out. I can keep the car going by revving the accelerator while stationary, and the car runs ok on the open road. It just seems to be that the idle speed is non-existent at first.
after about five minutes of driving (and after several engine stalls at junctions and traffic lights etc.), The engine seems to adjust to the idea of staying running, although the idle speed will still be very low. If I have been driving for a while, I get a warning light for engine electronics. Any time I take the car to a mechanic they dont seem to know what the problem is. Any ideas?