surging (hunting) idle when cold....

Something to think about - IAC's will tend to gum up from oils, dirt, and carbon. As long as they are warm they will work just fine as the rotating or sliding valve can move freely and rapidly when the system demands a specified position. In cold conditions the oils and gumming will become less viscous and cause the valve positioning to stick or be slow and affect the engine's capability to achieve a stable idle. Cleaning them may fix the issues.
 
ttmott said:
Something to think about - IAC's will tend to gum up from oils, dirt, and carbon. As long as they are warm they will work just fine as the rotating or sliding valve can move freely and rapidly when the system demands a specified position. In cold conditions the oils and gumming will become less viscous and cause the valve positioning to stick or be slow and affect the engine's capability to achieve a stable idle. Cleaning them may fix the issues.
Click to expand...


excellent thought....makes a lot of sense...thanks....I will check and clean them this WE.....

cliff
 
does anyone know if i can manually extend the sliding valve of an IAC so that I can fully extend it out to clean the entire shaft of the valve?.....if not any ideas how to get it to fully extend?....

thanks....

cliff
 
CliffA said:
does anyone know if i can manually extend the sliding valve of an IAC so that I can fully extend it out to clean the entire shaft of the valve?.....if not any ideas how to get it to fully extend?....

thanks....

cliff
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I don't think so; I believe the Mercury IAC's are PCM driven stepper motors and can only be positioned using the ECU. Maybe simply remove the IAC and look in it to see how crapped up it is and clean with a good aerosol carburetor cleaner. Might have to spray some in, let it set for a while, then flush out with more cleaner.

Keep in mind also that the ECM maintains pulse code count on the IAC stepper motor to know where the valve position is and for various reasons can loose position knowledge of the valve. For example when power is lost to the ECM (like disconnecting the battery) the ECM drives the valve fully closed when the key switch is first turned on then opens fully to establish valve stroke position relative to stepper count then sets a nominal cranking position.
So, have you tried to completely remove the power to the engines and allow a reset of the IAC's? As another note turning the battery switches off will not completely remove power from the ECM's; only way is to fully disconnect the batteries.
 
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ttmott said:
I don't think so; I believe the Mercury IAC's are PCM driven stepper motors and can only be positioned using the ECU. Maybe simple remove the IAC and look in it to see how crapped up it is and clean with a good aerosol carburetor cleaner. Might have to spray some in, let it set for a while, then flush out with more cleaner.
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10-4......thanks.....

cliff
 
since I cannot extend the pintle all the way out would you recommend using a light penetrating oil such a '3 in 1' oil instead of a heavy oil to lubricate the shaft after cleaning it with throttle body cleaner?.....I'm thinking this may help ensure the oil gets past any seal on the shaft so the entire shaft is lubricated.....

cliff
 
I would think any kind of oil would attract dirt, maybe some kind of silicone and maybe use contact cleaner to clean it as its made more for electrical components than is carb cleaner.
 
I looked at the Merc Service Manual and it has a write up for cleaning the IAC.....it does not mention using any oil probably for the reason atrick mentioned....

here is the IAC cleaning instructions from the service manual in case someone following this thread wants to clean their IAC valves:

cliff

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Cliff, I've been following this. I hadn't put my .02 in as others have given you great advice. After re-reading the thread something jumps out at me from your first post. After going to the gas dock and leaving the engines running all that time the issue went away. That tells me the engines are now thoroughly warm. In cooler weather the coolant temps may reach operating temps but that doesn't mean the engines are fully warm. take a lot more to heat all that iron.

I had this happen to me on my first Sea Ray but it was carbed so I didn't think it to be the same. The more I read the thread and thought about it I think it is that the engines are not fully warmed up yet.

I would still clean the IAC's cause it can't hurt.

Good luck
 
sdarc said:
Cliff, I've been following this. I hadn't put my .02 in as others have given you great advice. After re-reading the thread something jumps out at me from your first post. After going to the gas dock and leaving the engines running all that time the issue went away. That tells me the engines are now thoroughly warm. In cooler weather the coolant temps may reach operating temps but that doesn't mean the engines are fully warm. take a lot more to heat all that iron.

I had this happen to me on my first Sea Ray but it was carbed so I didn't think it to be the same. The more I read the thread and thought about it I think it is that the engines are not fully warmed up yet.

I would still clean the IAC's cause it can't hurt.

Good luck
Click to expand...


thanks Steve.....the engines not being fully warmed up could also fit into the scenario of a sticking IAC valve.....if the IAC pintle has 'crud' built up on it the cold weather could make the sticking of the pintle worse by not allowing the pintle to slide in and out of the throttle body easily....as the engine fully warms up it is possible the 'crud' on the pintle is also warming up and allowing the pintle to slide in and out of the throttle body more easily.....

cliff
 
Not sure I would assume warm crud is a lubricant. If in fact it is your IAC they usually develop their problem by not extending or retracting within themselves, not getting snagged up in the TB bore. How far they extend is measured in counts, and the scan tool will give you that number.
 
scoflaw said:
Not sure I would assume warm crud is a lubricant. If in fact it is your IAC they usually develop their problem by not extending or retracting within themselves, not getting snagged up in the TB bore. How far they extend is measured in counts, and the scan tool will give you that number.
Click to expand...


thanks....wasn't really referring to warm crud as a lubricant....more like it as being 'less restrictive' concerning the movement of the pintle.....if cleaning the IAC valves has no effect on the issue and the voltage test of the TPS looks OK i'll call in the mechanic for a scan of the engines...

cliff
 
to close out this thread, between crappy weather and family obligations over the past several weeks I finally had some time to work on the engines.....I cleaned the throttle body, flame arrestor, and the IAC valves on both engines but that did not help.....since the TPS were original and have internal moving parts that can and do wear over time I decided to replace the TPS on both engines to establish a baseline for these important sensors....this cured the problems with the port engine but not the starboard engine.....I decided to also replace the IAC valve on the starboard engine and this cured the problems....

so the 'cure' for the surging and stalling was a combination of IAC valves and TPS.....after also installing two new serpentine belts due to some 'chirping' from both engines that increased belt tension would not stop we took the boat out this WE for about 3 hours and all went well.....

cliff
 
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