Maxxum 5.7L Mercruiser Very High rev at "idle"

by Craig
(Oconto, WI)

Maxxum 5.7L Mercruiser

I replaced the linkage on the throttle body (the old one broke last fall, and I had to make a new one as they are out of production) and now when I start the engine, it seems like it goes to WOT, but the butterfly valves are closed! The linkage doesn't seem to be causing it, but that is the only thing I changed. I'm thinking it must be a vacuum leak, but I can't locate any, and the rev seems way too high for most common vacuum leaks. I'm wondering if it might be a sensor? If I shift it into gear, it continues at high RPM. Any thoughts about what to look for? The boat had a new crate engine installed in 2014.