On my 500 efi. I newly this year have that beep alarm going off... looks like it stops when shutting off port engine
so looked at my water temp and was fine, oil pressure and drive lub oil level were fine as well... as far as I know, there is only 3 reasons for the alarm to beep right?
anything elae makes the alarm to sound?

i plugged the computer tonight and found one code :34 map low, but guess what ! On my center engine!

anything i am missing before sending it to the doctor?

You will have to disconnect each sensor one at a time.
Also, an IAC that is going bad will sometimes cause this.

TPS on those? My 575's were based on those motors originally and I have issues w mine about once a year. Beeps about every minute or 2 when going bad.