HIGH IDLE: 1998 TBI 5.7 EFI Mercruiser. I keep getting a high Idle when warmed up...

[JohnEGraham]

1998 TBI 5.7 EFI Mercruiser. I keep getting a high Idle around 1100 after running the boat. On start-up, I get the usual high idol when it warms up and drops down to 800, but after I am running the boat around and slow to dock it doesn't drop down, it stays up at 1100. I tried putting it to neutral and revving it up and down to get it to slow up but it doesn't
I adjusted the Cable and added 5 rotations to the cable ( which was replaced a few years back) also replaced the Idle Control valve TCP and the PCV valve and checked vacuum hoses ( which aren't many since it's Electronic fuel injected)

Thanks

 

[Scott215]

Are you sure thottle body is closing all the way, very easy to check
It may need to be cleaned

 

[scoflaw]

Vacuum leak

 

[JohnEGraham]

Are you sure thottle body is closing all the way, very easy to check
It may need to be cleaned

Cleaned from outside

 

[JohnEGraham]

Found the Throttle body gasket mostly dissolved, so Air was getting sucked through.
Don't know why they make these gaskets out of a little more than card board?
The gasket given to me by the company who rebuilt the Throttle body was twice the size of the actual stock gasket so it looks worst than it would, but it did work for 7 years...

 

[Scott215]

Use a flap wheel and clean well ,then shop vac the whole intake