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High idle on GT40 after WOT run. |
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Mpost 
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Joined: July-05-2018 Location: Monticello, MN Status: Offline Points: 329 |
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 Topic: High idle on GT40 after WOT run.Posted: June-19-2020 at 4:41pm |
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This is not a great concern at this point but just curious if anyone has fixed this type issue on their GT40.
98 SN that has been running great all season. Wife pulled me for two runs this morning and I decided to see what my GT40 with a 422 prop would pull. (discussion on another post last week)  Went for a spin around our small lake and had it up to 44 MPH (on the air guides) and 4,700 RPMS for about 30 seconds. backed off and headed for the dock. When I came in at idle it was definitely fast and showing about 1200 on the tach. In neutral it would go up to 1500. Back in gear and tried burping the throttle a couple of times and it came down to 1000 in gear, 1300 in N. Let it run for a minute and still would not come down anymore. Shut the engine off, started it again within 30 seconds and it was back to 6-700 idle in Neutral. Had this happen once before early this year when running near WOT for a stretch. did not do any detailed fiddling but it was fine the next time I started the boat. Is this possibly the IAC or just a quirk of the. Thanks for listening and any ideas you have. Love CCF  (edit) boat is a 98 not a 99. changed this post to reflect that. |
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84 SN Sold 98 SN Lund Pro V 1975 Alumacraft
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KENO
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Joined: June-06-2004 Location: United States Status: Offline Points: 11112 |
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Posted: June-21-2020 at 2:51pm |
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I don't think I'd be worried quite yet.
Maybe check that your throttle cable isn't letting the throttle body butterfly valve hang open slightly. |
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Mpost
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Joined: July-05-2018 Location: Monticello, MN Status: Offline Points: 329 |
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Posted: June-22-2020 at 10:38am |
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Ken,
Thanks,. I'll look at that. I did replace the throttle and shift cable two years ago. |
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84 SN Sold 98 SN Lund Pro V 1975 Alumacraft
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Mpost
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Joined: July-05-2018 Location: Monticello, MN Status: Offline Points: 329 |
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Posted: June-27-2020 at 6:12pm |
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Looked at throttle cable and butterfly. All is working fine without the engine running. The throat and butterfly were a bit dirty so after spraying a little carb cleaner in and wiping clean with a rag, I then noticed this sticker on the outside of the throttle body.
 What is this special coating and what have I done now???? edit, I did find this post but no real answer in it.  Post 
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84 SN Sold 98 SN Lund Pro V 1975 Alumacraft
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KENO
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Joined: June-06-2004 Location: United States Status: Offline Points: 11112 |
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Posted: June-28-2020 at 2:03pm |
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I think you're screwed now, you dissolved the special high tech anti loping compound that's on the throttle blade
 What I really think is that you didn't hurt a thing by spraying some cleaner in there. I hope I'm right |
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Canuck-Surfer
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Joined: September-14-2019 Location: Ontario, Canada Status: Offline Points: 222 |
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Posted: September-19-2020 at 2:13pm |
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I’m sort of in the same boat I am cleaning everything up. I had a crazy amount of gunk in the IAC. I went to start removing the flame arrester to clean the throttlebody and saw the sticker. I’m guessing since Keno said it’s OK, it’s OK?
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1996 Sport Nautique GT40 EFI
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Gary S
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Joined: November-30-2006 Location: Illinois Status: Offline Points: 14096 |
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Posted: September-19-2020 at 3:59pm |
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Tough call. I have a 95 GT40,no sticker, a 95 5.0 "Volvo" throttle body with no sticker,complete intake from a 98 GT no sticker and a complete 99 GT40 with no sticker. Did you clean the screen under IAC valve? Maybe just take a rag soaked in cleaner and clean as best you can rather than spray
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KENO
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Posted: September-19-2020 at 7:37pm |
KenO says................Mpost sprayed his to clean it so if you were to ask Martin if he damaged anything that would be a logical thing to do He also thinks Martin probably didn't damage anything and he may not have cured anything either Lots of people have sprayed their throttle bodies trying to cure one problem or another
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Mpost
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Joined: July-05-2018 Location: Monticello, MN Status: Offline Points: 329 |
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Posted: September-20-2020 at 8:53am |
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Don't know that it hurt anything and did not help anything other than make it cleaner. I didn't get crazy when spraying cleaner, just moistened and wiped with a rag till clean. Didn't touch the IAC either.
Dont know if I took any special (invisible) coatings off when I did this or not? Or if they were already gone from someone else cleaning it?
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84 SN Sold 98 SN Lund Pro V 1975 Alumacraft
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Canuck-Surfer
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Posted: September-20-2020 at 11:42am |
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I ended up wiping it down with throttle cleaner on a cloth. It was filthy. Didn't seem to hurt anything.
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1996 Sport Nautique GT40 EFI
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slmskrs
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Joined: January-03-2012 Location: SF bay area, CA Status: Offline Points: 522 |
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Posted: September-23-2020 at 9:33pm |
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So, I assume nothing further on why it is idling high after WOT run. I don't recall the exact RPM if you remove the IAC (Idle Control Valve?). But if it removed and the engine started, it will idle somewhere in the 1200-1440 range. If the ICV somehow got stuck open, that could cause it.
Also, you said it looks like the butterfly valve closes (when off). Can you pull the spark arrester off (keep your fire extinguisher handy), run it WOT (same conditions) and then (while running), check the position of the butterfly valve/linkage?
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Gordon '97 Ski Nautique, GT40
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Canuck-Surfer wrote: