350 mag won’t idle nor start without throttle

pog mo thon

pog mo thon

Member
Aug 20, 2008
177
Metedeconk river, brick NJ
Boat Info
sea ray 320 sundancer v-drive
Engines
twin 350's
Hi,

My 2007 320 sundancer with 5.7 350 mag inboards won’t start without throttle or stay at idle if I don’t manually position the throttle at 600rpm. The boat runs fine after that but it will die if I push the throttle back all the way back down even with warm engines.
It originally started with the starboard engine but within a few weeks same thing happen to the port.
I have changed both”twice” OEM IAC and mufflers with no change. Mechanics scanned but no error showed up, no error on SmartCraft either. I Just change the fuel filters and cap and rotors with no change at all.
Please if someone had the same symptoms please help me!
It has the newer cool gen 3 and new injectors done a few years ago.
I haven’t change the plugs or wire yet but I have little hope it will change anything.

thank you for your help!
 
I believe you were right. The throttle bodies were very dirty and after cleaning them I got my idle back!!!
interesting thing though, coming out of plane back to idle, the RPM got stuck at around 1200 and got me sweating for a minute!!! Took it out of gear and rev’ed up a few times and I got it down to 750, a little hard shifting but it got me back to the dock safely.
I am going to try spraying that seafoam now. For some reason I have a lot of black dust and gunk around the air filter.

thanks
 
pog mo thon said:
I believe you were right. The throttle bodies were very dirty and after cleaning them I got my idle back!!!
interesting thing though, coming out of plane back to idle, the RPM got stuck at around 1200 and got me sweating for a minute!!! Took it out of gear and rev’ed up a few times and I got it down to 750, a little hard shifting but it got me back to the dock safely.
I am going to try spraying that seafoam now. For some reason I have a lot of black dust and gunk around the air filter.
thanks
Click to expand...
"black dust and gunk around the air filter"
Check your belts and clean your "flame arrestors".
 
could i use compressed air and the sea foam to clean up the passages
 
yes i have the same problem with my port engine. At start up when cold i had to give it some throttle to start. then when engine reached operating temp it would idle, however now its not idling at all please reply thanks. oh i did replace the iac sensor and no change.
 
pog mo thon said:
I believe you were right. The throttle bodies were very dirty and after cleaning them I got my idle back!!!
interesting thing though, coming out of plane back to idle, the RPM got stuck at around 1200 and got me sweating for a minute!!! Took it out of gear and rev’ed up a few times and I got it down to 750, a little hard shifting but it got me back to the dock safely.
I am going to try spraying that seafoam now. For some reason I have a lot of black dust and gunk around the air filter.
Click to expand...

You might wanna take off the flame arrestors, and with the engines off -- push the throttle-only button and advance them forward so the throttle plate in the TB is open. Then clean the sides of the ports but also the faces and edges of the throttle plates with carb/TB cleaner If there's build-up they can stick open or closed.
 
do you recommend crc throttle body cleaner and compressed air please reply thanks
 
I would only spray into the TB or used compressed air if the TB is completely removed from the engine.

If you need to clean it in-place, I would spray cleaner onto a rag and then apply. Otherwise you run the risk of pushing debris into the intake. My 2 cents .....
 
does the throttle positioning sensor and temperature sending unit affect the cold starting cycle.
 
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