Idle air controller maintenance

[Dave R]

I was at the Wolfeboro docks last Sunday afternoon and tried to start my Mercruiser 7.4MPI engine so I could leave. The engine would turn over normally and fire but would not stay running. It would just sputter a bit and die after I released the key. I decided to pull the idle air controller out and see if there was a problem with it and if so, if there was anything I could do about it. Fortunately, I had the necessary tool and it is very easy to access right on top of the engine. Turns out it was gunked up with fine particulate matter (dust) and stuck nearly all the way out (which would severely limit the amount of idle air available). I exercised it a few times to get it unstuck and put it back in. The engine fired right up and ran normally.

I'm not 100% sure my IAC failed due to dust or if there is something else intermittently wrong with it, so I bought a new one and will clean and keep the old one as a spare. Mercruiser and Volvo use the same style IAC (they come with the GM motors) on all their fuel injected engines, near as I can tell. If you have a fuel injected engine, you might want to add cleaning the IAC to the list of annual maintenance chores. Our flame arrestors make pretty poor air cleaners so the IAC is likely to get dirty on a boat. If you do need a new one, there's no difference (in construction or price) between an automotive or marine part, so they can be sourced at any auto parts store.

For reference: The IAC is just a small, electrically-operated, variable air valve that bypasses the throttle body. The engine computer uses it to control the amount of air the engine gets at idle (and that controls the idle speed). With the IAC wide open, my engine will run at about 2000 RPM with no load; closed, it will not run at all.

[challmec]

good morning Dave
thanks for this great piece of info. I will surely place this in my pre season checklist..have a great week