Mercury 300 XS stalling on idle

[bep078]

A friend of mine has a 2010 300 XS with 125 hours and recently the motor has been stalling when idle. Over 2000 rpm, the motor works fine. WOT rpm is normal, mid range and top speed is normal. The idle rpm is always ranging from 500 to 600 rpm and sounds erratic. (it sounds as if it misses a beat every few seconds or so) I performed an induced missed fire test. It was noticeable when I cut off the ignition for each individual cylinder so coils seem to be fine.

I have a video of air and fuel pressures when running and after the motor has been turned off.

https://www.dropbox.com/s/mknjw84o7o...26.23.mov?dl=0

Anyone can provide some insight?

Thanks.

[Turborr]

My engine sounded like that when I had 2 stuck air injectors. Does every now and then a puff of smoke come out of the exhaust?