2007 Volkswagen Jetta 2.5 Engine

3 weeks ago the car let out a huge cloud of light blue smoke at start up. It will intermittently smoke at start up, and if you drive at a constant speed, you can feel the motor stumble and it will start to smoke, if you step on the gas, it will clear out and drive fine. Sometimes it will do this 3 or 4 times a day, other times I can drive 2 days with nothing. The oil was changed the week before this started, and I was told that it was probelly overfilled, and would need a pvc valve replacement, which is built into the valve cover and would cost $700 at dealer where the oil was changed at. They also are saying it could be a cracked ring, but wouldn't the smoke be constant if that was the case?

Thanks, Darin