I have a 97 baja 322 with 502 mags the starboard engine after a few hours of driving does not like to idle. It will start right back up and run fine for a few minutes but will then stall again. If I give it throttle I can get it on a plane and it will run fine. There are no codes.
Im thinking if theres no codes its a fuel delivery issue. if it was vapour lock im thinking it wouldnt start at all.

its pretty annoying at the dock or ramp

It's probably the cool fuel system. Very common issue with those motors. Do a search and you will see all the symptoms and fixes. It's and pain in the azz and not a cheap fix.

Is the idle surging before it stalls? The reason I ask is because the IAC motor is a very common failure on these engines. Do a search for 502 IAC and you will find a ton of people (myself included) that had to replace this part. It is a tiny little stepper motor that is mounted behind the throttle body. You can get the Mercruiser part for around $100 or go to Autozone or Checker and get the GM part for around $25 which is what I did. Either way, a $25 part and about 10 minutes is worth it even if it's not the problem.

Thanks for the replys I have already changed the iac when the motor wouldnt idle a while back. I was under the impression if the motor had a vapour locking issue once it stalled I wouldnt be able to restart or if it would I would have no power. This isn't my case. My next plan was to instal a carter marine fuel pump to act as a lift pump for the efi pump. I have fuel flow meters so I can't run the return direct to t he tank

I have the exact same problems with my buddies boat, both engines do it too. I replaced one ECM, it was bad, I put a fuel pressure gauge on it and it did not drop,IAC's are working and checked the timing as well. Can't understand this either.

Had a similair problem with my 502 mag, replaced IAC, problem still there. Finally replaced electric fuel pump in VST seemed to cure the problem........but it wasnt cheap if thats not the problem.

I was lucky enough to have cool fuel setups on my boat. But I think im going to try the lift pump idea and see what happens