intermittent idle stall

[msballin]

Good Morning -

I posted this situation several weeks ago and had mechanic check my port engine. Upon analysis he felt as many of you did that it was IAC issue. To confirm, he switched air intake manifolds (put starboard on port) and she started right up. He then replaced the IAC on the other engine (which now had the air intake from the port engine) and all was fine. To summarize and hopefully not to confuse, the port engine now has the original IAC from the starboard engine and the starboard engine has the new IAC.

Well last evening the port engine (which has the original IAC from the starboard engine) stalled at idle as it had previously. My question is, how likely is it that both of these IAC valves would need to be replaced somewhat simultaneously? Is this purely coincidental or do they go after a certain amount of usage? Also, is it possible that there is some other issue which may be causing these valves to go?

Sorry to be so wordy, just trying to offer as much info as possible. Thanks much as always.

Mike

 

[Morpheus]

These are a common item that goes out. On the Merc 5.0L MPI engine they are very easy to change not sure about your engines but MANY of the members here carry extra IAC's with them as spares on their boat. I just had mine changed since the mechanic noticed a bit of above normal exhuast and he said that's a good sign it's on it's way out so I had him change it and show me before it went out.

 

[msballin]

Thanks Morpheus. They're not that easy to get to. They are behind the flame arrester which is blocked by the raw water exhaust hose. Need to remove air intake manifold and such. Wish I had known of your answer before so I could have had the mechanic change both of them at the same time. Appreciate your input.

All the best,

Mike

 

[daddyox]

Mine went within 10 days of each other, at about 175 hours. I have a spare I keep on board now.

 

[Turtlesboat]

Just replaced one yesterday. Weeeee.

 

[Double D]

I had this problem several months ago. As it turns out, the connections (I believe it was the fuel pump relay)on the wires leading to the fuel pump were corroded causing the fuel pump to stop after a few minutes of running. The engine would usually start back up, then quit after a few minutes. It took the mechanic a couple hours to find the problem. The connections were located on the lower, starboard, forward side of each engine. I have a '99 310 Sundancer with 350 V Drives.

 

[Larry]

MSBALLIN,

I missed this thred the other day, I have the same problem on the same motors. How did your mechanic get the throttle body off? You can't get it off without removing the exhaust elbow or removing the whole MPI plenum.

 

[Morpheus]

Sounds like the 7.4's are harder to deal with on the IAC then the 5.0MPI. My IAC is right under the flame arrestor just 3 allen head screws and it's off, sounds like the 7.4's require removing more then just the flame arrestor to get the IAC changed.

 

[fc3]

The 7.4 has a very robust IAC, unlike the ones used on the later engines, which are crap. Replacing the IAC on the 7.4 Horizon engine required the removal of the throttle body, since the IAC is mounted low on the unit. The 7.4 MPI has the IAC on the top. Just Ducky has her original IAC on both engines. I don't know anyone with a 7.4 who had to replace on yet.

Best regards,
Frank

 

[msballin]

Larry,

He removed the air intake manifold which covers the engine in order to get at it. You need a set of torque bits to remove it and once he got the manifold off all seemed pretty easy. The part is around $90 and it shouldn't take more than an hour to replace. Hope this helps.

 

[Brian]

I think I might have the same problem with the port engine on my 2004 340. It cut out on me on Lake Ontario. Had an AOU alarm go off. Could restart the engine but would stall as soon as I backed off the gas. Mechanic thinks its a Mass air-fuel solinoid, but sounds more like the IAV valve to me. Any thoughts out there?