Help.....502 mag
 

I have a 502 mag EFI that runs great and has 47hrs on it. The last two times I've been out on the water and while at idle it will ramp up about 300 rpm and holds and wont come back down . When I shut it down and recycle the ignition it wont do it again for awhile. There are some days it does it several times and some days it dosent do it at all. Any Ideas???

Welcome to the board! I have no idea....... :(

Probably the IAC going bad. You are best off to run a scan tool on the engine.

It is likely to be the Idle Air Control. It has a little plunger that gets carboned up and will stick. You might try taking it off and cleaning with carb cleaner. If that fixes it, buy a new one because the bild up will return. Also clean the port it goes into real well, build up there can cause an idle problem too. When you turn the engine off the IAC resets itself, which is why it seems to fix itself.