Trouble starting/low idle

[Freedom rec]

I have a 05 22v with the 350 merc. It is having a bit of trouble starting initially. Once I get it stated it runs great most of the time. I had it quit on me twice yesterday when I shifted it into gear. The idle seems really low 400 or so. Any ideas? The voltmeter fluctuates substantially with rpm variations, this leads me to believe that it could be a worn out battery. (this boat has only one) Although the battery seems to have plenty of cranking power... I have not had any time to mess with it yet, so any info would be helpful. Thanks

[R&T Babich]

I think ours idles around 600 rpm.
Your IAC may be dirty and need cleaning.
When you say the voltmeter "fluctuates substantially" what does it do exactly and at what rpm?
At 400 rpm the alternator is not outputting anything so the voltmeter will read around 12.4v.
Around 600 rpm the alternator will kick in and bring the system voltage up to around 13.5v.
It may go up to a little over 14v if the battery is really low.
Do you keep a battery maintainer on it?

[dogbert]

If you think it's the battery, try charging it with a slow (2amp) charge overnight and see if that makes a difference.

As for the starting troubles, I'd check your distributor cap. Mercs are notorious for issues with the distributor cap. That would explain the initial rough idle and difficulty starting.

[Freedom rec]

What is the IAC? 400rpm seems really low but it is not a rough idle. Seems like it used to idle arround 600rpm. I noticed the voltmeter showing <12volts at idle and >14+-.5 at full power. Also on the inital start I have to add a little fuel to get it going. Again it starts fine after it has been running, the only exception it the 2 times it quit out on the lake after about 2hr running. The engine has about 330 hours on it. Thanks again I should also add that the battery is 1.5 years old, and I have never put a charger on it.

[Freedom rec]

Ok I had some time to look at this today, and I have concluded that the battery is not the problem. It looks like it could be the IAC valve. I unplugged it and and saw no difference in the idle. Im going to order one tommorow, unless anyone thinks there could be another problem. Thanks for your help...

[chpthril]

Ok I had some time to look at this today, and I have concluded that the battery is not the problem. It looks like it could be the IAC valve. I unplugged it and and saw no difference in the idle. Im going to order one tommorow, unless anyone thinks there could be another problem. Thanks for your help...

Uh, that would be normal! The IAC is stepper motor that is controlled (driven electrically) by the ECM. It only moves when voltage is sent to it by the ECM, if unplugged, no signal is reaching it so it stops where it is and does not move.

[chpthril]

What is the IAC? 400rpm seems really low but it is not a rough idle. Seems like it used to idle arround 600rpm. I noticed the voltmeter showing <12volts at idle and >14+-.5 at full power. Also on the inital start I have to add a little fuel to get it going. Again it starts fine after it has been running, the only exception it the 2 times it quit out on the lake after about 2hr running. The engine has about 330 hours on it. Thanks again I should also add that the battery is 1.5 years old, and I have never put a charger on it.

When you say you "add fuel" to get it going, what exactly do you mean? opening the throttle or actually pouring fuel in the throttle body?

upon initial start, what is the engine's rpms?

[dogbert]

Sounds like a fuel supply issue. When was the last time you changed the fuel filter?