Avensis New Engine And Oxygen Sensor?

[zaf50]

Hi all, Had a brand new engine fitted to my 1.8vvti avensis and full service inc brakes and tyres which has been in my garage for 2 years.

Now first few drive vehicle was juddering especially on bends, steering wheel itself does not tremor.

More recently when on the dual carriageway engine management light came on and vehicle driving much the same.

Now have been informed that suspect oxygen sensor fault, how can I diagnose and where to get from cheap has this car is costing very much if from the web which website?

Would also the discs cause it to judder has if soemthing is stopping pulling otherwise in straight line very little juddering smooth ride, comments appreciated

What is the MAF?

Regards