IAC Valve

aero3113

Like I said above, I ’m not 100% sure but I think I remember reading that was a major difference between the auto and marine IAC’s.

Spyderweb

Whoa, so is Merc putting auto IAC's on new motors then selling us expensive marine ones for replacements?

aero3113

I wouldn’t say that yet, I’ll look further into it and see what info I can find. I was thinking the same with the PO’s shop...

JimGuy341

I'm doing an IAC replacement this weekend.  Once the new one is installed, is there anything special I need to do?  Or do I just turn the key and start her up?

aero3113

Just start her up!

YYZRC

I bought the windstar IACs and they look just like the new one @aero3113 posted - brass pin with spring wrapped around it.  They idle too fast - 900 RPM at start up, settles in to around 700 RPM after warming up.

STANDARD MOTOR PRODUCTS

AC423 did not work for my boat.

halifax212

Same thing happened to me. Spend the extra $125 and go OEM. Problem solved. I keep the automotive one on board as a spare since I could not return it.

YYZRC

Yeah, season is too short to mess around. I ordered the Merc unit this afternoon. Apparently it’s back ordered. 

212rowboat

lots of talk about IAC's when the IAC rarely fails on its own. 

all that thing does is allow metered air into the TB to allow idle with the blades of the TB closed... that's it.  It adjusts throughout it's life and in varying conditions to maintain a steady idle...... it adjusts to what? air flow.... bad air flow.. two causes of bad air flow- dirty filters and dirty TB's.... the IAC drifting that plunger into and out of the hole to maintain a prescribed RPM (or range) becomes difficult when it has to move a lot, and it has to move a lot because it's gummed up, being gummed up disallows the plunger to move within the range expected by it's tiny little motor and they either burn that motor up or the plunger loses it's 'mapping' or calibrated position... 

replacing an IAC on a car doesn't happen that much... a matter of fact, it happens most often when someone has taken it off and 'cleaned' it- moving the plunger and losing its 'map'... why is that so? because- cars burn hotter and that heat sinks right up to the TB and varnishes the gummy crap that builds on boats TB's.  also, in a car, you're more likely to swap air filters more often. 

clean your TB's.  it doesn't take a lot of effort.  make sure and clean the orifice the IAC occupies inside the TB's throat to make sure gummy crap isn't slowly covering it (which makes the IAC work a lot harder than it should).  Clean or swap your air filter/flame arrestor... if you 'really' want to be clever, cut a section of tubing and affix it to your IAC 'breather', remove it's filter, and direct that tube to the air hat/flame arrestor on the filtered side much like your PCV is (but on the inside not the out)... 

a little bit of throttle body cleaner goes a long way...  

LaRea

When the IAC fails, is it a gradual fail, or immediate?  What I mean is, does it give you any warning before failing?

Ian

2 beeps every minute from my experience. 😁 but sounds like maintenance can prevent it. 

212rowboat

LaRea said:

When the IAC fails, is it a gradual fail, or immediate?  What I mean is, does it give you any warning before failing?

not really.... it's designed to meter the air and reconcile with the CPS and TPS to achieve a certain RPM.  when it starts to wear out there will be momentary struggles to idle... it's a device that does a good job of covering issues until it can't any more- and then that issue becomes apparent all at once... the issue is dirty TB's and/or gummed up IAC ports in the TB, or, dirty IAC filters (that you have to ask yourself 'how did they get so dirty')... 

q: how did they get so dirty? oily and trapping crap?
a: check your PCV valves, y'all.. take them out and shake them... they should rattle.. if they don't rattle they are stuck... if they are stuck they aren't allowing blow by crank case gasses to enter your air hat, and that has to go somewhere as the pressure pushes past valve cover grommets, and where is there air sucking (an IAC is basically a metered vacuum leak)? straight into that little filter, gumming it up- making the plunger have to open further to allow the same air into the TB as recognized by the CPS and bounced off the TPS- making that plunger work harder... wearing it out faster.  

rasbury

I just installed an IAC filter as there was not one in it!

Cableguy Greg

LaRea said:

When the IAC fails, is it a gradual fail, or immediate?  What I mean is, does it give you any warning before failing?

Mine was immediate. Failed right before I was coming into a harbor. Had very low idle and stalled going in and out of gear. Replaced with OEM and boat works great. (Knock on wood) 

Ian

Cableguy Greg said:

LaRea said:

When the IAC fails, is it a gradual fail, or immediate?  What I mean is, does it give you any warning before failing?

Mine was immediate. Failed right before I was coming into a harbor. Had very low idle and stalled going in and out of gear. Replaced with OEM and boat works great. (Knock on wood) 

Same here a couple of years ago heading into a lock. Checked today and I do actually have filters there.

YYZRC

Mine was surging between 300-600 rpm at start up. That is now gone. 

212rowboat

fellers, y'all just 'think' it was immediate.. it was a while in the works, and you just didn't realize it.  It takes time for it to get to the point it's beyond it's parameters, but it only takes a second for it to finally give up the ghost. 

If you add cleaning the TB and area to your ten hour maintenance list you'll be better served than waiting for things to go wrong- simply spray some throttle body cleaner directly into the throat of your TB, making sure to douse it evenly all the way around and the butterflies too, and you'll find a lot of idling and throttle response questions will disappear..... just don't try to start it right after this... wait at least ten minutes or so.  If you're 'really' motivated, you can use compressed or canned air to dissipate the solution, too... once the runoff hits the floor (plenum plate) of the intake manifold it can't really do your TB or AIC any harm....

it's also a good time to inspect your air filter/flame arrestor and IAC filter.... and PCV valves.  those PCV valves that connect to the air hat/flame arrestor are a good bit of the 'problem' with IAC's gumming up (and TB's becoming nasty).... if possible (it is on mine) have those PCV valves dump into the airhat on the opposite side of the IAC (or as far as you can get them from it).... depending on how much blow by your engine generates, it's beneficial in some applications to install a little catch can with a filter to actually capture the oil and solvent (exhaust gasses) laden blow-by with that can/filter.  You just have to dump it every or every other oil change.   

YYZRC

Agreed. I cleaned my TBs over the winter and they were disgusting!! The butterflies were completely caked with about 1/16” of greasy dust.