I have a 1994 Mercruiser 502 motor (fuel injected) which is having some problems which I have no idea how to resolve. The boat runs great for a good part of the day. I will turn the engine off for 30 or 40 minutes and try to start the engine. The engine will start up with no problems but it will run really bad. The motor sounds like a lean popping with no black smoke. If I feather the throttle for a min or two the motor will pick up and start running normally for the rest of the day. Someone told me that it sounds like a carbureted motor with a bad vacuum leak when experiencing this issue. Someone also told me that I had a bad Idle air motor. I replaced it and am still having the same problem.
I had another issue as well. after running the motor for a good part of the day it wouldn't start. I had to hold the throttle open all the way and crank it to get it to start. After it started it ran perfect.
I'm not sure why it is acting like this because when the motor is running it is running great. If anyone has any ideas that I could try I would really appreciate it. I just bought the boat and want to get this fixed.