2007 Malibu Wakesetter 247 with 8.1L running very rough until it warms up completely

[AlabasterBobby]

Hi all, first time posting here.  I recently bought a 2007 247 with 8.1L and it runs very rough for about the first 10 mins but once it warms up it runs great for the rest of the day (even after a 2 hour rest).  It idles a little rough but when I attempt to throttle up it runs extremely rough and will not even accelerate past about 10 MPH.  If I back off and let it idle then it will run fine after about 10 mins.  This past weekend I replaced the spark plugs and coolant sensor but I haven't water tested yet (I will test it this week).  I've also seen many post about IAC  sensors failing but I can't figure out the location of the IAC on this boat.  If anyone can help me diagnose the issue at hand and also if anyone has a diagram of the IAC location than I would appreciate it.  Thanks

Edited July 12, 2021 by AlabasterBobby

[justgary]

42 minutes ago, AlabasterBobby said:

Hi all, first time posting here.  I recently bought a 2007 247 with 8.1L and it runs very rough for about the first 10 mins but once it warms up it runs great for the rest of the day (even after a 2 hour rest).  It idles a little rough but when I attempt to throttle up it runs extremely rough and will not even accelerate past about 10 MPH.  If I back off and let it idle then it will run fine after about 10 mins.  This past weekend I replaced the spark plugs and coolant sensor but I haven't water tested yet (I will test it this week).  I've also seen many post about IAC  sensors failing but I can't figure out the location of the IAC on this boat.  If anyone can help me diagnose the issue at hand and also if anyone has a diagram of the IAC location than I would appreciate it.  Thanks

I would clean the inside of the throttle body.  Pay attention to the edge of the butterfly and where it hits the throat.  You might have good luck by opening the throttle so you can spray the edges and the side channels.  The IAC should be on the side of the throttle body, but I really don't think that is it since it gets better when it is warm.

I was going to suggest the temperature sender (the one for the ECM if you have two), but hopefully that is the one you changed.  Other than the TB clean, I wouldn't do anything until you water test again.  Running on a flush attachment in your driveway should tell you a lot also if you can do that.

[Fffrank]

Also do the cap/rotor if it's been a little while.  Regular maintenance items.