Intermittent vibration/mis fire?

[Mr Med]

Hi,

Apologies, I’m new to this.

My 2013 2.0TDI Avant starts and runs great. Issues occur on longer journey, motorway steady speed. First time I thought I was getting a front flat. 
vibration through the car/steering. Not a flat. Re started and drove on, issued cleared. No fault shown. Subsequent times I thought it might be a mis fire but if I select neutral(auto gearbox) engine revs freely and I still feel vibration through steering/car.

Garage says can’t identify until fault light comes on!
 

Help much appreciated.

[Steve Q]

Could it be an issue with the maf sensor or cam sensor? I'd appreciate both should throw up a fault code. 

[Mr Med]

Thanks Steve, I’ll pass on to garage.