2004 mercruiser 4.3 mpi will not start at idle or stay running at idle

[knelson1913]

I've been a reader here for a long time but this is my 1st question. My 2004 Mercruiser 4.3l mpi has been running great for the last 2 years (since we bought it), but yesterday we took a cruise around the lake at idle speed which took maybe 1-1/2 hours and all of a sudden the alarm goes off and my gauge says check engine. The gear lube reservoir is at the full level and the engine oil says full on the dipstick, so the only thing I can figure is it is overheating. The temperature gauge reads 139 degrees which seems low for an overheating. Let it set overnight and I cannot get it to start without throttling up, and it will not run at idle. I put the muffs on it today because I was concerned water was not circulating but with the muffs on I could see that it was. Does anyone have any suggestions?

 

[Fun Times]

Hi there, welcome to iboats!

Keep in mind that there are many other sensors that will sound the warning horn on your engine model.

Sounds like you might have a problem with the idle air control (IAC).

If so, you'll want to check to see if the throttle body, IAC inlet hole, IAC muffle (if you have one) and flame arrestor is dirty and clean as needed. If that don't do it, then testing the IAC valve may be the next item on the list to inspect.

Also your engine temperature seems a little low, you should be closer to the 160-170 degree range. Your thermostat may be showing it's age.

To help with finding your correct parts catalog for your engine model, your engine serial number would be needed.

 

[knelson1913]

Not sure if this is the number or not, this is the only number I could find on it. 4.3L Alpha 864270-007 892204

 

[achris]

What is the alarm? Is it a couple of beep each minute or a steady alarm, or a beep every second? (2 beeps a minute is likely to be the IAC, as FT suggests, but the only way to be conclusive is to put a scan tool or the PC based diagnostics on)...

 

[Fun Times]

Sorry, but those are not the serial numbers needed, they look more like part numbers.

The serial number should be either on top of the engine someplace with a sticker or a metal tag mounted to the starboard side of the engine block located just above the engine starter motor. It should start with something like 0M or 0W and 6 numbers after it.

http://www.perfprotech.com/blog/articles/mercruiser-serial-numbers