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5.0 mpi unsteady idle

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XS POWER

Regular Contributor
5.0 mpi will idle all day at 1000, drop it to 800 it will idle happily then stumble to near stall then pick back up to 800. There is no pattern to it, sometimes happy then not. New IAC valve. Showing no codes. Cheers
 
XS POWER said:
5.0 mpi will idle all day at 1000, drop it to 800 it will idle happily then stumble to near stall then pick back up to 800. There is no pattern to it, sometimes happy then not. New IAC valve. Showing no codes. Cheers
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One item that frequently comes up with mpi is the failure rate of the crab style distributor cap. Might be worth looking at or replacing if an issue is causing the ecu to move the advance around at idle
 
Dieter said:
One item that frequently comes up with mpi is the failure rate of the crab style distributor cap. Might be worth looking at or replacing if an issue is causing the ecu to move the advance around at idle
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Thanks Dieter, I will put that on the list. Its a mates boat .,I am going down on Tuesday have a look at it. The engine was just out of it for starter repair and other repairs. Could an ground or wiring issue be a cause?
 
XS POWER said:
Thanks Dieter, I will put that on the list. Its a mates boat .,I am going down on Tuesday have a look at it. The engine was just out of it for starter repair and other repairs. Could an ground or wiring issue be a cause?
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I have read the MPI's can get funny of voltage is low, so for sure as a sanity check and tighten positive and negative cables at both battery and engine contact points. Look for any loose grounds
 
The tech that done the work is blaming the wiring under dash from what I have been told, Can I start motor unplug cannon plug to eliminate that wiring. It was running fine when it went in there so I find it hard to believe that is a problem but it is a boat after all chit happens.
 
I'd bet the dash wiring has no impact on the idle instability on a MPI engine...I'd encourage your mate to start searching for another tech...
 
Yea bud not much to choose from here unfortunately that's why I am here trying to get idea's before Tuesday. Thanks for the replies
 
Thanks Chris and appreciate your time,The IAC was supplied and fitted by the last Tech. I will read up on reindexing and give it a go.
 
XS POWER said:
Thanks Chris and appreciate your time,The IAC was supplied and fitted by the last Tech. I will read up on reindexing and give it a go.
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Where did the last tech get the IAC? Automotive IAC will not work on this... I don't care what anyone tells you, the PWM% will be way to high with the auto parts store equivalent.

Look for Mercruiser Service Bulletin No. 2011-11R2 The procedure starts on Page 14. This part of the bulletin is for all flat cap HVS(distributors)...
 
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