thanks, yes it is real and real and only knocking sound, the car is extremely in good condition no crankshaft bushes or camshaft bushes loose. also connecting rods are all ok.
I did recognize all types of sounds,
now why I changed MAF , when I press accelerator some time engine stops, in this situation it do severe knocking at low RPM less then 2000 . it can happen if no signal from MAF when accelerator is pressed , and no increase of fuel supply from injectors, in this case car will hesitate to increase RPM.
still I have doubt on MAF. I have no reference for this as I could not found service manual for N BOX. but yes MAF is giving 1,4 volts in Idle and by pressing accelerator it is increasing to 2,3 Volts.
my both MAF are behaving the same way.
some time it works perfect for 20 days then it again start knocking engine stall at signal by pressing acceleration.