I took it to a local garage today. The diagnostics showed a misfire had occured on cylinder 2. Unfortunately i forgot to ask for the excact code. They deleted to error code to see if it made a difference and when i took it for a test drive it seemed ok again for a while so i decided to leave it at that until there was a problem again. So driving back from the garage the light came up again at hard acceleration. What's interesting though is that now it disappears after restarting the car but before i had the fault code deleted, the light came up immediately after starting the car absolutely every time. I wonder if it could really be the valvetronic motor? I also found some sort of fix for a common fault in with the valvetronic motor:
http://mhhauto.com/printthread.php?tid=1744