7.4 MPI IAC Replacement?

glenncal1

glenncal1

Active Member
Nov 6, 2009
158
colorado
Boat Info
2000 380AC
Engines
Twin Merc 7.4 Horizons
I have 7.4 horizons. Do you need to pull the throttle body assy to change the IAC? If so is it a big deal? Thanks
 
glenncal1 said:
I have 7.4 horizons. Do you need to pull the throttle body assy to change the IAC? If so is it a big deal? Thanks
Click to expand...

Just did this on my 7.4 MAG MPI Horizons (see 370 thread for details). IAC is on the underside of the throttle body and cannot be accessed from where it is. I saw it as two choices: 1) remove exhaust elbow, riser, and exhaust hose to allow flame arrestor to be removed so that throttle body can be removed; or 2) remove plenum in its entirety and flip it over and there it is (you still need to remove flame arrestor and throttle body to access both IAC mounting screws). I went with choice 2, and bought the plenum gaskets (4 gaskets in a kit), as there is a good chance these gaskets will stick and be destroyed when the plenum is removed. You will also need a stud removal tool ($15 at Autozone) to remove the throttle body studs. After doing it 4 times, i got the whole process down to about 30 minutes to change the IAC. Good luck.
 
Depending which year, some are mpi and horizon manifold is different, and depending on trans/drive being used it may have the elbow in the way of "just"removing.
 
Sublimetime said:
Depending which year, some are mpi and horizon manifold is different, and depending on trans/drive being used it may have the elbow in the way of "just"removing.
Click to expand...
True story. If you have v-drives, then the engines are facing backwards, so the elbows are turned around vs. straight drive like you would find in an EC. Further if you have elbow risers (mine are 6") to get rid of the log exhaust in favor of water lift mufflers, the problem is further compounded. I found it much easier to just lift the plenum, and put it on the bench. Your studs for the throttle body air inlet are likely going to need some persuasion to come out. I'd be willing to bet that your 380 AC is V drives, and you have riser extensions.
 
No, straight drives. Very easy to get to flame arrestor/throttle body. I will look for the stud removal tool. Is there a specific name for it?
 
Vice grips and Aero-Kroil and patience. Perhaps double nut the end and use a long wrench.
Or, they might come right off. Had one stud that was so locked up, I put the stud in a bench vice and turned the plenum for leverage.
 
370Dancer said:
Vice grips and Aero-Kroil and patience. Perhaps double nut the end and use a long wrench.
Or, they might come right off. Had one stud that was so locked up, I put the stud in a bench vice and turned the plenum for leverage.
Click to expand...
Is the corrosion a salt water issue? Hoping
 
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