One For Spannerman?

[paultallett]

I wondered if I could pick your brains over an issue with my 2003 350 MAG MPI please? Recently when out running we got a twin warning ping every minute from the guardian system, all appeared normal so we carried on to our berth before a closer inspection. On trying to berth my idle revs were all over the place with the engine also stalling, this lead me to believe that the IAC was the cause of the fault? It has stuck before and I carry a spare one for this reason.

On changing over to the new IAC the warning pings were gone and she held revs and idled fine, the only issue being warm idle has gone from 600 to 800 rpm. As a double check I did put the old IAC back on and the warning ping returned along with the rough idle.

Would anyone have an idea as to how I can get the warm idle rpm back to 600 please? I'm aware that the idle speed is controlled by the ECM and wondered if the new IAC needed calibration?

I've checked that the throttle is closing fully, my next step was to pop some gasket sealer on to the new gasket, making sure it wasn't sucking a small amount of air in? Any suggestions would be greatly received

 

[Bajansailor]

In case he doesn't happen to see this thread, this tag should (I hope) alert him to it - @spannerman

 

[spannerman]

Just saw your post, you are on the right track but there isn’t any calibration procedure for the IAC, normally they are just plug and play. But it sounds like you may have an air leak, the only way to be sure us to see what the duty cycle is on the IAC to see if it is over compensating, but you need the Mercruiser diagnostic kit to read that.

 

[paultallett]

Thanks both, really appreciated the replies.

The new IAC isn't OEM (although sold as a direct marine replacement) so I'm beginning to wonder if that might be the issue in itself? Adding sealant to the gasket has made no difference, where else should I be checking for an air leak?

In the past I have watched a Mercruiser tech plug a tool in that did alow him to make the idle speed go up and down, I'm guessing this is what you're referring to Spannerman?

Thanks once again.

 

[spannerman]

Yes its a programme we have on a laptop, the only other place air can leak in is the vac hose to the fuel pressure regulator.

 

[paultallett]

Thank you, I'll look it to it and see what I can find.

Really appreciate the help.

 

[stelican]

I wondered if I could pick your brains over an issue with my 2003 350 MAG MPI please? Recently when out running we got a twin warning ping every minute from the guardian system, all appeared normal so we carried on to our berth before a closer inspection. On trying to berth my idle revs were all over the place with the engine also stalling, this lead me to believe that the IAC was the cause of the fault? It has stuck before and I carry a spare one for this reason.

On changing over to the new IAC the warning pings were gone and she held revs and idled fine, the only issue being warm idle has gone from 600 to 800 rpm. As a double check I did put the old IAC back on and the warning ping returned along with the rough idle.

Would anyone have an idea as to how I can get the warm idle rpm back to 600 please? I'm aware that the idle speed is controlled by the ECM and wondered if the new IAC needed calibration?

I've checked that the throttle is closing fully, my next step was to pop some gasket sealer on to the new gasket, making sure it wasn't sucking a small amount of air in? Any suggestions would be greatly received

What is the IAC

 

[paultallett]

It's an idle air control valve

 

[paultallett]

@spannerman sorry, a couple of more questions if I may?

I've identified the vac hose and all appears well, is there a way you would recommend testing for a leak? Also, if I manged to beg or borrow a TechMate tool, reading the online instructions I see the section about testing the IAC, obviously this would check to see if the IAC can get the engine to idle at 600rpm, would you then be able to 'set' that as the final rpm?

Many thanks.

 

[spannerman]

The IAC is not adjustable so the diagnostic tool won’t help. It will only show you the percentage of duty cycle its working at. The ECU tries to keep the idle at 600 by varying the IAC, there is no means of resetting/adjusting it as its either right or wrong. In the throttle body there is a small port that goes to the IAC, there is a sponge filter in the opening, check this isn’t clogged, it is a Service item.

 

[paultallett]

That's great thank you. I'm going fit an OEM IAC, new sponge filter and then go from there is the way forwards... fingers crossed that gets it nailed.