how to remove throttle body 1997 454 mag mpi

[larry1954]

Does any one know how to remove the 4 studs that hold the throttle body and which appear after removing the flame arrestor on a 1997 Mercruiser 454 mag mpi? I have tried multi grips, a stud removing tool and also tried to lock two nuts together on the thread and undo the inner one. Nothing seems to work. They are either on very tight and I should use more force with the stud remover or there is some other trick I do not know about.

I am trying to get at the IAC valve, since I seem to have an idling problem.

 

[achris]

Hello larry1954, and :welcome: to iboats...

Hopefully, AllDodge or tpenfield will be along to help out. I'm pretty sure they're done this job...

I assume you're referring to item 37 in this drawing....

Cheers,

Chris......

 

[tpenfield]

:welcome: . . . Larry

I used vice grips and really had to clamp hard on the studs to get them to break loose. Clamp right up close to the throttle body and take a good bite into the stud. Then a couple of whacks on the end of the vice grips with a hammer. The part of the stud that goes into the plenum is a coarse thread as compared to the end where the cap nuts are fastened, which is a standard thread.

You will want to put a dab of grease on the coarse threads when you re-install them.

 

[larry1954]

Yes, achris, it is 37 that I am trying to remove.

Thanks for that info, tpenfield.

 

[alldodge]

Agree, vice grips or small pipe wrench.
Sure hope someone has not used red loctite on the threads previously. If someone has used lockite you may need heat to break it free

Another option is to remove the plenum (screws 22 and 23) and then replace the 4 square gaskets (item 18) upon re-install.
https://www.mercruiserparts.com/bam/.../31810/2336/14

 

[larry1954]

Thanks for your suggestions also, ALLDodge.

I just succeeded in getting them out. Tried the vice grips and pipe wrench, but no success, so went back to my stud remover tool and placed it up toward the throttle body which I had not done before and it worked.

Now I am trying to remove the IAC. I have removed the one screw that appears to hold it in place, but what happens now? Should it just pull out? Or do you try to lever it out with a very small screwdriver?

 

[larry1954]

I have checked the coil resistances on the IAC and appear to be getting about 51 ohms for each coil. Sound like it is faulty?

I have managed to lever the IAC out a bit with a screwdriver. Just have not got it all the way yet.

 

[larry1954]

Finally got the IAC out - did not notice that there are actually two small screws holding it (one underneath the gasket).

So how do I check if it is faulty? Resistances between the two pairs of pins appear to be about 51 ohms. The valve itself does not seem to move at all. Should it be able to be pushed in against the spring?

 

[achris]

.... Should it be able to be pushed in against the spring?

I'm not familiar with this particular IAC, but all the others that I have dealt with do move quite freely... The coil resistance sounds a bit high, but again, not played with that particular one. It would be worth squirting some throttle body/carb cleaner into the IAC and see if it frees up. If it does, you win...

Chris......

 

[alldodge]

IMPORTANT: DO NOT use cleaners containing methyl ethyl ketone. It is not necessary
for cleaning throttle bore and valve deposits.
IMPORTANT: DO NOT allow the TP sensor and IAC valve to come into contact with
solvent or cleaner.

CLEANING AND INSPECTION
1. Remove and discard sealing O-ring from IAC valve. Clean sealing surfaces, pintle valve seat, and air passage with a carburetor cleaner to remove carbon deposits, being careful not to push or pull on the IAC valve pintle. Force exerted on the pintle might damage the worm drive. DO NOT use a cleaner that contains the extremely strong solvent methyl ethyl ketone.
NOTE: Shiny spots on the pintle, or seat, are normal and do not indicate misalignment or a bent pintle shaft.

The IAC is a worm drive so don't push pull on the tip nor use carb cleaner on it. You can use carb cleaner on the TB

Reset IAC valve pintle position as follows:
a. Turn ignition key ON for ten seconds.
b. Turn ignition key OFF for ten seconds.
c. Restart engine and check for proper idle operation

Have not found a ohm test but tpenfield has don some other testing

 

[larry1954]

Thanks for all that. I connected up the IAC valve and turned on the ignition and it moved outwards. So I am thinking that it might work.

However, i notice that the pintle has some corrosion on it. I notice also that there appears to be a slight nick out of the area where it seats in the TB and that the corrosion on the pintle more or less corresponds to the nick in the TB. Could this be the idle problem? I have attached some pictures:

Could not add the pictures. Need a web address and used photobucket and it shut down my computer.

 

[larry1954]

Here is another go at the pictures:

https://photos.google.com/photo/AF1QipMFVxBFjJCIv-3HAaT-OESxBLVNiWfLWGRKFHVV

https://photos.google.com/photo/AF1QipNx04mD_ULNoALbOUluTMvBvqr3cdK_ER3nSdVh

https://photos.google.com/photo/AF1QipNx04mD_ULNoALbOUluTMvBvqr3cdK_ER3nSdVh


https://photos.google.com/photo/AF1QipNhy_6MAso3HAd7WRWBIeFm9NNvgodZyUZWqyIg

I wonder whether that nick at the bottom of where the IAC valve seats is normal?

 

[achris]

Here is another go at the pictures:

https://photos.google.com/photo/AF1QipMFVxBFjJCIv-3HAaT-OESxBLVNiWfLWGRKFHVV

https://photos.google.com/photo/AF1QipNx04mD_ULNoALbOUluTMvBvqr3cdK_ER3nSdVh

https://photos.google.com/photo/AF1QipNx04mD_ULNoALbOUluTMvBvqr3cdK_ER3nSdVh


https://photos.google.com/photo/AF1QipNhy_6MAso3HAd7WRWBIeFm9NNvgodZyUZWqyIg

I wonder whether that nick at the bottom of where the IAC valve seats is normal?
[IMG2=JSON]{"data-align":"none","data-linktype":"1","data-size":"full","src":"https:\/\/photos.google.com\/search\/_tra_"**[/IMG2]

[IMG2=JSON]{"data-align":"none","data-size":"full","src":"https:\/\/photos.google.com\/search\/_tra_"**[/IMG2]

can't see those pictures either. Error 404.

 

[larry1954]

Do not know what is going on there. The links work for me. I could PM them to you?

 

[larry1954]

Looking again at the TB, that 'nick' at the bottom of where the valve seats looks deliberate and original. So I wonder whether it is the rust on the surface of the pintle that might be causing the problem with the idle. Sandpaper it clean again or replace the IAC?

 

[achris]

Looking again at the TB, that 'nick' at the bottom of where the valve seats looks deliberate and original. So I wonder whether it is the rust on the surface of the pintle that might be causing the problem with the idle. Sandpaper it clean again or replace the IAC?

When it's such a difficult part to get at I have a philosophy. "If in doubt, chuck it out"...

Chris.....

 

[alldodge]

What are the symptoms which caused the IAC removal?

If the IAC or seat has damage there will be idle issues

 

[larry1954]

Symptoms were stalling when put into gear, often when cold (trying to back the boat off the trailer) and sometimes even when the engine was warm. Idle seemed also to be unstable so that when you increased revs to about 2000 rpm (out of gear) and suddenly cut them back to idle, it would sometimes jump around a bit from 500 rpm to 700 rpm, and sometimes just stall when it when down to the 500 rpm. As if the ECM could not work out the correct idle speed.

 

[Fun Times]

The valve itself does not seem to move at all. Should it be able to be pushed in against the spring?

This design IAC is called a stepper motor. Though not all that much recommended to move by hand if you planned to hope to try and reuse the original IAC....The way to move it by hand would be to pull and push while twisting the pintle as it is magnetic inside the unit like shown within the following video of your design IAC motor at about the 3:00 mark....,https://www.youtube.com/watch?v=qMAUBU-6ErY

It still takes some heavy effort to move the pintle by hand even while turning.....If you're unsure the IAC is the issue but want to try another one at a more cost efficient way then you could try finding one at a local auto parts store as finding one off a GM engine should be a match....Just be sure the IAC motors wire plug connection of the IAC motor is orientated in the correct location that matches your old one so it easily plugs back in....There are two designs making it near impossible to plug the wire back in if you find the incorrect IAC motor.

805224A1 = https://www.ebay.ca/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=805224A1&_sacat=0

https://www.youtube.com/watch?v=yHgTRyfkXxs
https://www.youtube.com/watch?v=MwNuZRtAyco
^ And/or search online GM IAC Stepper Motor.

The service manual recommends while installing the throttle body, Apply Loctite 242 to threads of studs. Using a stud driver, torque studs to 165 in. lbs.....Also it recommends a stud driver for removal. The flame arrestor nuts are said to also use Loctite 242 and tighten to 50 in. lbs.

Cycle the key ON and OFF with a 10 second wait time before starting the engine after installing.

 

[alldodge]

Your symptoms would lean me toward the IAC. I would replace it at this point if it was mine. FT has posted some good info