Idle problem

[Rvp]

I have a 2002 mercruser 5.7L. Has a TBI throttle body. Idle surges up and down from 800rpm to 1500rpm. When move the throttle control at the throttle body it changes but can't stop surge. Is that we're the idle control sensor. Could it be defective.

 

[Tassie 1]

It could be defective
but it could also be that the " mesh filter " is blocked and needs to be cleaned,

could be something else again,

l had a similar sounding problem with a 2013 5.7 mpi mercruiser,
replaced it with a new unit and new mesh,
fixed my slow rough idle problem

not saying it will fix yours but worth looking into it

 

[alldodge]

Remove the IAC (Idle air control) valve (item 7) and the IAC muffler (foam piece Tassie 1 mentioned) and clean with soap and water. Don't use things like carb cleaner, it can damage it.

https://www.mercruiserparts.com/bam/subassembly/31886/4856/130

 

[Rvp]

In trying to find problem. Disconnected the map no change,disconnected air flow no change, disconnected idle control small change. Then reconnected idle control idle normal. And stayed that way. Was able to get the boat out of the water with no problem. Question where is this mess filter?

 

[alldodge]

Inside the throat of the TB, see foam piece on top

 

[QBhoy]

I’m quite unfamiliar with the tbi if that means it’s an EFI and thinking on it, not even sure it has an idle air control valve...it likely does. If so it’s worth a go at replacing it...but also worth noting that it could also just be doing its job in an effort to counter another problem which is causing the change in idle, making the IAC fight to counter act. Just a thought.