350 mag mpi surging idle

gherkingherkin Member Posts: 45 ✭
in Rinker Express Cruisers Forum
All.  So I’ve been working all summer to get this engine rebuilt.  Pretty much got all the bugs worked out.  Except I am getting a surging idle occasionally only when not in gear.  I replaced the IAC.  This engine is the one with the plunger that goes into the side of the throttle body not the iac on top.  Engine is virtually new throttle body was cleaned and all new gaskets.  Anybody got any ideas of the best way to figure this one out? 
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  • gherkingherkin Member Posts: 45 ✭
    edited October 2020
    Some updates.  When I turn my key on I always get a double tone. And then often right at startup it will double tone again and then all is good.  Was reading and some say that I should only get a single tone when turning key on and a double means I have codes. So borrowed a friends reader and hooked it up.  Had several codes and cleared them. Also adjusted my throttle body to be sure it was closing all the way.  The reader had an iac reset function so I ran that for the heII of it.   Then took for a test ride.  Still seem to have a bit of a surge when starting or when revving in neutral but it tends to straighten out in a few seconds and then all is good.  So there is definitely an improvement.  I am still getting a double tone when turning key on but reader says I have no more codes after test run.  So not sure about that but things are definitely better off now.  Just gonna run it some more and see how it does 
    Post edited by raybo3 on
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  • reneechris14reneechris14 Member Posts: 3,134 ✭✭✭✭✭
    Sometimes the IAC are bad out of the box. Is the channel for the air to the IAC clear?
    2005 Rinker FV342  Pawcatuck river,Ct
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  • stuckmotostuckmoto Member Posts: 13 ✭

    I had a IAC fail this summer. Got the double code, engine would stall at idle. Noticed when replacing the IAC that the connection was loose(tab broken?) so I secured it with a zip-ty. All good.

    So two things - is the connector corroded? Have you tested the TPS? I believe that the IAC gets a signal from ECM when the throttle body goes full closed. Have you verified that? They may be fighting each other. <---just any idea

    2003 270FV 350mag/B3
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  • davidbrooksdavidbrooks Member Posts: 1,399 ✭✭✭✭
    The other thing to look for is to make sure all your vacuum hoses are connected. On my last boat i knocked one off and it was acting almost like a bad iac.
    It's 5 O'Clock Somewhere!
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  • YYZRCYYZRC Member Posts: 5,143 ✭✭✭✭✭
    PCV valve?
    2008 350 EC on Georgian Bay
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