Rough idle & engine stall at idle

[9452772]

Hi all,

    Looking for some ideas before I head back to the shop.  I have a 2003 LSV 23 with the Indmar Monsoon 335 engine (750 hrs).  This past spring the engine had a hard time idling while getting ready for summer.  I took it to the shop and they advised new plugs, wires cap and Idle control valve which was all replaced.  Went to the lake a few weeks back and had a very hard time keeping it started.  Once it warmed up seams to be sorta fine but would die at idle.  When I got back I bought a new idle control valve and new throttle position sensor.  I changed those and I shorted out the A/B pin to put boat in service mode.  I pushed throttle all the way forward and back.  Went to the lake and same thing, stalls at idle and hard to start.  I would have to start quickly get into gear to go or it would stall.  At cruising / pulling speed boat is fine.

 

Any ideas before I head to shop and loose a few more weeks of summer?

 

Thanks,

[justgary]

The first thing I would do for any idle issues is thoroughly clean the throttle body, including the butterfly and the IAC chamber.  The little bypass passages in the throat at the edge of the butterfly get filled with gum and carbon, restricting critical air flow at idle. 

After you clean it if still won't idle, come back and we can help you throw parts at it. 

[9452772]

Update,

 

    I took the throttle body off to clean and it was already very clean.  I did spray it down real good and removed the Idle control valve and cleaned that area.  Let it dry out real good and re assembled.  I then put boat in service mode, turned key on, moved throttle all the way forward and back.  Took boat out of service mode.  I did adjust the idle set screw up a little.  Started boat and it idled at about 1200 RPM till temp reached 160.  At that point I started to slowly adjust idle back down and just under 1200 it start to surge.  I backed idle off a little more and the boat does what it has been doing lately which is surge between 500 and 1500 until it dies.  Start up again with same surge a few times then dies.  Forgot to mention in my original post above that the knock sensor has also been replaced.  Any help would be appreciated.

By the way, should there be a gasket between the throttle body and the upper intake that it mounts to?

Thanks,

[Steve B.]

Following.

[justgary]

It would be really useful to get some data from the engine while it is running since this could be several things.  I think a 2003 uses MEFI 4, but I'm not sure.  

Just to make sure we're thinking about the same setup, yours does have a plenum cover and the throttle body on one corner, not a regular looking intake manifold with the throttle body stacked in the center, right?

[9452772]

Sorry took so long to get back with everyone.  Yes this engine has the offset throttle body with the intake filter pointed slightly down.  I plan to remove the throttle body one more time to double check every little bit of dirt is out if there is any from my first cleaning.  I did notice when I took it off there is no gasket between the throttle body and the main intake.  should there be a gasket?  If so can someone help with a part number or place to buy it as I have not been able to find a gasket that looks like it would fit my throttle body.

 

Thanks all,

[9452772]

Any help would be appreciated.  I take the boat to the shop so anything I can pass along to the shop would help.

 

Thanks,

[thequink]

Any updates on this? This past week my boat had an issue on start-up, the idle jumped up and down 400-1500 rpms until it died. Restart and only goes for a second. Then won't start. Come back 30 min later and it runs normal. Only repeated the issue once in a whole week at the lake. 40-70 degree temps, so don't think it's vapor lock. Knock sensor? Temp sensor? 

[9452772]

My issue ended up being a missing gasket between the throttle body and intake manifold.  The first shop most have not put the gasket back on and also stripped two of the throttle body bolts.  the second shop discovered the missing gasket and heli coiled the bolt holes.  Problem solved.

[justgary]

Wow.  What a find.  I'm glad you got that one squared away.