2000 Jetta hesitation at acceleration

Up until this week I've never had a problem with my Jetta. However, it's been in the shop everyday this week. Problem started with the check engine light going off. Then hesitation upon acceleration when the car is cold. My mechanic replaced the O2 sensor and it starting running even worse than before. Just about didn't make it to work this morning. Took it back to the shop. Decide that the only thing left to do is replace the Master Air Flow Sensor to the tune of $300 plus labour. So I did some research and called VW this morning and it seems that they've extended the warranty on the MAFS to 7 years or 115,000kms here in Canada and the equivalent in the U.S. So if you start getting a stuttering or hesitation when you accelerate, call your VW dealship with your VIN# and you'll probably still get it under warranty.