Raise the idle on a 5.7 mpi
08-13-2015 | 03:52 PM
#2
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Joined: Jul 2011
Posts: 9,594
Likes: 45
From: Ft. Worth TX
On stock MPI Merc and all other OEM stock MPI engine apps Idle speed is non adjustable. If you are having problems with low idle speed there is a reason for it and or a problem that needs to be addressed .
08-13-2015 | 10:14 PM
#5
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Joined: Jul 2011
Posts: 9,594
Likes: 45
From: Ft. Worth TX
Not if he has ECM 555
So with that said what exactly do you have and your set up along with the ECM
Do you have alpha or Bravo outdrive ?
Too high of idle is an alpha outdrive killer another reason why Mercruiser recommends and keeps idle speeds at the 600 to 700 rpm's.
Was your cam changed in this app
have you pressure tested the exhaust manifolds and riser together ?
What exhaust system do you have here ? Merc OEM dry joint manifold & riser ?
Is your exhaust thru the prop or silent choice or straight out transom ?
A lot more info needed -
Possible need riser extension blocks as your waterline to relation to the boat / exhaust is too high
Have no idea what you have here so throwing out some ideas
So with that said what exactly do you have and your set up along with the ECM
Do you have alpha or Bravo outdrive ?
Too high of idle is an alpha outdrive killer another reason why Mercruiser recommends and keeps idle speeds at the 600 to 700 rpm's.
Was your cam changed in this app
have you pressure tested the exhaust manifolds and riser together ?
What exhaust system do you have here ? Merc OEM dry joint manifold & riser ?
Is your exhaust thru the prop or silent choice or straight out transom ?
A lot more info needed -
Possible need riser extension blocks as your waterline to relation to the boat / exhaust is too high
Have no idea what you have here so throwing out some ideas
Last edited by BUP; 08-13-2015 at 10:30 PM.
08-14-2015 | 07:43 AM
#7
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Joined: Dec 2013
Posts: 358
Likes: 2
From: Minneapolis, Mn
Go to your tool box and find your cordless drill, next find the biggest drill bit you have. Drill one hole on the top side of the intake manifold, that should let just enough air in to raise your idle.
Like many have said your idle is set(adjusted) by the ecm thru the IAC motor.
Like many have said your idle is set(adjusted) by the ecm thru the IAC motor.
08-14-2015 | 09:20 AM
#9
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Joined: May 2012
Posts: 135
Likes: 0
From: portsmouth rhode island
The motor is a bone stock 5.7 mpi 330hp with a new stainless marine exhaust system that is 6in taller and has longer risers made to help stop the reversion. I've been having this problem since day one. I had a thread going on this topic while ago with little success. I had the heads repaired cause of valve seat damage. After a day of running I check the exhaust the port side will be dry but the starboard wet. After I flush the motor both are wet but if I keep the rpms up they're dry.
