1999 502 mag Efi, Bought boat with motor out,reinstalled new motor but it runs at WOT at start. Have tried to shut down and restart but get the same thing. Anyone have any advise Thanks

I am sure that you checked the obvious, like sticking or mis-adjusted throttle cables... So, after that, I would scan for codes with the engine off, take a good look at the I.A.C. count and the t.p.s. The I.A.C. should be somewhere between 20 and 40. The t.p.s. should be a low percentage about 5% at idle. If you don't have a scanner, I would pull the I.A.C. motor and check it out.

ok ty checkmate454. But what the helllllll is a I.A.C. and what should I took for ty

I have to ask the obvious. Pull the flame arrestor off. Are the butterflies open or closed?

I think EFI is the operative letters in his description!

An EFI still has butterflies, GLH.

(and they are behind a flame arrestor)

Also, a vacuum leak could cause the motor to run at high rpm on startup, too. WOT startup would be a scary ordeal...

Not really,,, EFI has butterflies also,,, got to control air somehow now dont you?

Shows you what I know!!!

Do a search here for IAC... or TPS...
There is a thread I wrote on how to check & adjust the TPS & IAC, also how to test the IAC motor....
It is in the tech Q&A section.