Hi
I've had this too. Experience has taught me it can be one of two things - one which you can fix, the other is a garage job.
The easy fix is a problem with your engine management/throttle. Polo's are fitted wither with a "fly by wire" throttle, or with a halfway house - a throttle that uses a conventional throttle cabel to the pedal, but ALSO has a motor fitted to the throttle valve..so the ECU can open the throttle if it thinks the engine is about to stall.
The first step is to clean off any gunge and muck that may have built up in and around the throttle. Visit your local Halfords and buy a big aerosol of Wynn's throttle cleaner (dunno the exact name but its a bloody big can, and the small print will tell you its perfect for our needs). Remove the airbox totally, start the engine, and spray into the throttle. DON"T BE CONCERNED if the engine labours or cuts out. So would you it you'd had pressurised solvents sprayed down your throat! On a serious note, do avoid breathing the spray because it is NOT NICE AT ALL.
If possible, stop the engine, then manually open the throttle valve and spray down into the manifold. You should be able to see all the black deposits dissolved away, leaving a throttle that will not catch on any build-up of crud. It'll take about 15 mintues to totally evapourate off.
NOW - reset your ECU. Do this by disconnecting the battery, count to ten, then reconnect it. Reset your radio security code

and then start up and go for a drive. Give it about 15-20 miles and the ECU will have relearnt your engine's character and will hopefully manage it accordingly.
The other possibility is a knackered sensor, be it engine speed, throttle position sensor or similar. These all mean a trip to a garage - basically cos they aren't things we mere mortals can fix....
