Hiya Pete, 90% sure its MAF. Volts at idle are about right, volts under a sharp sudden type acceleration should be very near 4.0 volts. Wide open throttle while not under load will not give you the best reading. Not advisable either, maybe bugger up the new timing chain! Best would be live readings on the road. I have had that many problems with these MAFs that I now carry a brand new genuine bosch unit. Every time, I have sold the new unit!I must also warn you against any of the cheapies, they will come back to bite you!
If you do fit a new one, check the emissions, as they will probably go rich. ECU will have compensated for weak mixture and will continue to do so until reset, either by scanner or by driving the car for a few miles. If the car is due for MOT, say next day, it could possibly fail, Best Wishes, Gwyn