I had a similar issue just after I bought my gti. It would die every now and again and surge/lurch at about 2k rpms. If you have a boost gauge installed you can tell if its turbo lag, as it turns out mine was the crankshaft position sensor. If you read up on it, its a pretty common part that fails over time. It also isn't too spendy and you should be able to find it at either ecs or your favorite auto parts store. Good luck!