Loud air sucking sound

[BRODY]

Can you guys hear the air sucking into the engine? I thought it was alot louder this year then last. I cleaned the spark arrestor but no change.

I read some posts talking about a idle air valve? Just wondering if this is normal. Oh yeah it's a Mercury 350 mpi.

[Jason B]

No sucking noise on mine, maybe the Chicago smog thickens the air enough to slow it down so I can't hear it!? ;-)

[Fast1911]

It's hard to say, I can hear it on my 350mpi but it sounds like it always has.....with the engine cover open of course, can't hear it when it is closed.

[BRODY]

I don't want to take it to the shop, they will have it for a couple weeks.
I only have a month left of comfortable boarding!

[R&T Babich]

Ours is also very quiet.
Make sure the vacuum line to the fuel pressure regulator is still connected at both ends and check the throttle body mounting bolts/nuts.

[jwanck11]

I have the same engine in a D-Drive (right behind me) and I do not hear anything. Sorry I am not more helpful on a potential fix...

[BRODY]

Thanks guys, I'll take a look at all the lines and the throttle body mounting bolts tonight.

[jmstige]

I read some posts talking about a idle air valve? Just wondering if this is normal. Oh yeah it's a Mercury 350 mpi.

Now that you say this - when I took the valve off to clean it, I was fiddling with it and it pushed in and I was unable to pull it back to the original position. I proceeded to spray the carb cleaner and put it back on.

When I first started the engine - there was a loud sucking air sound for about 5-10 seconds and then it stopped. I assumed it was because I pushed the valve in.

I guess if the other suggestions don't work out you could look at this because it was real easy to remove and replace.

[BRODY]

Ok, I looked over every hose, made sure all passages were clear. Still loud sucking noise. I looked at the break down and I'm missing the muffler in the throttle body.

Now I noticed it being alot louder in Spring after I pulled it out of storage. I thought it was a bearing in one of the pulleys. After looking closer it was air sucking. It must have been removed when my shop winterize it, and never put back in? I'm going to give them a call today and see if they remove the muffler when they winterize.

[BRODY]

could that little $1.25 part make that much difference in the amount of air sucking noise produced? I guess I will find out.
Shop did not admit they removed it to winterize, but I did'nt expect them to.
Has anyone had experiance with the IAC muffler.

[philwsailz]

I will share that I too have a huge sucking sound with my stern-drive 5.7 liter MPI merc motor. It did not start making the sound until after I had the boat a while

My buddy at merc shared with me to check that the IAC was tight... IT becomes loose easily apparently...

I will be splashing it tomorrow for a weekday get together, so I will probably play with it then to see if I can determine where mine is making the sound. I hopfully will be able to shed some light...

[dogbert]

could that little $1.25 part make that much difference in the amount of air sucking noise produced? I guess I will find out.
Shop did not admit they removed it to winterize, but I did'nt expect them to.
Has anyone had experiance with the IAC muffler.

I would not think that this is something they would touch when winterizing so maybe it just fell out, like phil suggested.

[chpthril]

What is the current idle speed?

[BRODY]

Dogbert, I was thinking when they fogged the engine by spraying into the throttle body, it either came out or they removed it first so they did'nt get fogging oil all over it?

chptril, I'll have to check the rpms at idle, not positive what it is.

Any way I have the IAC muffler on order.

[philwsailz]

I would not think that this is something they would touch when winterizing so maybe it just fell out, like phil suggested.

A point of clarification. My Mercruiser contact suggested that the IAC itself was maybe loose. He thinkks maybe teh sucking sound is air going into the throttle body at a location other than designed, i.e. through a gap where the IAC attaches...