High rpms while idle

[Maxpowers1207 3]

I have an 04 cyclone with 5.7 350 mercruiser. Today when I put in neutral, it would the rpms would go up to 1300, but when I would put it in gear real slow they would drop to 900-1000.  Any ideas? I was about to put it away for the winter, but woul like to get this taken care of first. 

[rhino89523 34]

Here is where I would look. Vacuum leak can cause high idle. Idle is controlled by IAC, could be that, but also cable could be hanging. I would disconnect cable and see if idle returns to acceptable level, if it does, its the cable, if it doesn't I would probably be looking for a vacuum leak or the IAC could have pooped the bed.

My boat is the first FI boat I have owned, so I am no pro, but I play with cars so those are my guesses.

 

[Maxpowers1207 3]

3 hours ago, rhino89523 said:

Here is where I would look. Vacuum leak can cause high idle. Idle is controlled by IAC, could be that, but also cable could be hanging. I would disconnect cable and see if idle returns to acceptable level, if it does, its the cable, if it doesn't I would probably be looking for a vacuum leak or the IAC could have pooped the bed.

My boat is the first FI boat I have owned, so I am no pro, but I play with cars so those are my guesses.

 

forgive me for being mechanically simple, but what are you referring to with the cable?  The throttle cable?

[rhino89523 34]

Yeah throttle cable, if that thing isn't returning properly it can hang it open just a little on the plate. If you disconnect the throttle cable you would only be under the influence of the IAC...unless your perfect pass cable is hooked up and hanging. That's where I would start, make sure my cables are not hanging it up. If it's not simple like that my next guess would be vacuum leak or failure in the IAC.

I'm not a boat mechanic, I just do all of my own work on everything and thankfully my boats motor has not had problems yet so I am not intimately familiar with it yet like I am everything else I own. I am just trying to think of what I would probably be looking for if my boat had a hanging idle.

Search the internet for finding vacuum leaks will net you some interesting viewing. I believe smoke machine is the right way if you are a pro, propane and carb cleaner are the top choices for redneck methods....please don't use the starting fluid method...just sounds dangerous.