Hi

I have a 5.0 EFI Mercruiser engine on a 290 Sea Ray. When it is in idle and when switching from forward to reverse then back to idle position, the engine will rev up and down on it's own in idle and sometimes die. This is problematic when it comes to docking. I have changed the computer, the throttle body, the IAC valve, all the sensors from one engine to the other. I put new gas in it, checked the fuel pump and filter. I am out of ideas, my next step would be the wiring harness, what do you think?

Change your transom shift cable