1993 Range Rover Engine cuts out at 20 mph and also at 38 m

Hello, my boyfriends Land Rover will cut out at 20 mph and also at 38 mph, Also the check engine light comes on when the engine gets warmed up. Otherwise it starts and idles fine. It tends to cut out when he presses on the accelerator.

I am suspecting the O2 sensor but I am not sure whether it is or not, we are praying it isnt the MAF sensor (these are rather expensive!)

Thanks for your time.

From Sue