Originally Posted by SeaRenity
......Just to be clear, the IAC vent filter, also called the IAC muffler, is not the IAC. It is a filter for the IAC. It can get dirty and clogged.
Cost is about $2 each.
The IAC vent filter is inside the throttle body assembly and its easy to change. They are about $2/each. If what you say is correct, moving the throttles forward out of gear does not result in a improvement then let’s look a the rotor and cap.
First, go on another boat. See if your boat is cranking longer than other boats with the same engines.
If yes, then lets open the cap and look at the contacts. Use a tork screwdriver. Do you have a tork screwdriver set? Removing your engine cover, the big black rectangular piece of plastic on the top of your engine, will make access to the cap much easier. All your spark plug wires go to the cap. Just remove two tork screws and pull off the cap. No need to remove wires at this time.
You are very over due for a new rotor and cap. As odd as it sounds, low hours are harder on a rotor and cap then high hours. Lack of use causes corrosion. Winter storage causes corrosion. Only use prevents this corrosion. Mercury Marine recommends changing the motors rotor and cap every 3 years.
With the cap removed, turn it so you can look inside the cap. You will see little metal contacts. Do the contacts look clean or do you see corrosion? Look down at the rotor. You will see a metal piece that looks like a Popsicle stick. This piece spins around and makes contact with the metal contacts in the cap. How does this rotor look? Do you see corrosion? Are the outward corners shiny or black?
If you see corrosion, black tips or white residue, it is time to install a new rotor and cap.
How do you know the correct part numbers? Well, on your engine cover is your engines serial number. Write this down. Next go here: http://www.mercurypartsexpress.com/us/
Note: I am not saying to buy the parts at this website. In fact the prices are higher here than you can find elsewhere .This mercury marine owned website will help you find the correct engine part numbers.
Click on “Part Search by Engine Serial #” and enter your engine serial number.
After you hit enter, look for “Distributor and Ignition” most likely this will be on the second page. Now look for "Cap Distributor" and "Rotor." Now go shopping for these parts at your preferred supplier, internet discounter or local Mercury dealer. I recommend you stick with genuine Mercury parts for these items and I don’t say that for all parts.
With your new rotor and cap in hand:
You will need a tork screwdriver and paint pen or other device to label the spark plug wires.
Label your wires first; a paint pen works well for this.
Remove the wires from the cap. To remove the wires, grab the boot on the end of the wire, not the wire. Twist one direction then the other then twist again as you give the boot a pull. Remove two tork screws and pull off the cap. Two more tork screws and your rotor will come off. Next install the new rotor and cap and reinstall the wires. To get the wires back on, push them on as you listen for a snap or pop. After you do a few you will just get the feel of it. Do not skip labeling the wires. Get them back on in the same spot.
Even if your problem remains you needed to do these items anyways.
You are also due for new spark plus but let’s do one item at a time.