The solution is to check for fault codes. Do you know anybody with VAGCOM software? If you are in JHB and I can get my VAGCOM cable back from 20VT

, I could check it for you. Mail me.
Alternatively you can check for fault codes using the blink codes - see
http://www.sjmautotechnik.com/trouble_shooting/ecuf20v.html#fcs4 or
http://s2central.net/blinkcodes.html
BTW Does it only happen after you drive the car hard? Could be something to with overboost protection. It can also be the Hall Sensor that does not work when hot (therefore you have to wait for it to cool down). The only other problem I can think off hand is a MAF flow exceeded error.
Knowing these cars I have an idea that a boost leak could be the culprit somehow.