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Discussion Starter · #1 ·
Semi-new to the forums...unfortunately my first post has to do with my boat problem. (1999 454 mag) fuel injected. My idle is sticking @ 3000rpm and tends to stick when you run the motor hard (i.e. pulling a skier or tuber). Previously I could let the boat sit as in letting it cool off and I could manage to get the idle down to 1500rpm which is still too high to engage the transmission. So I read up on the internet and thought I had the problem solved by narrowing the symptons down to what I thought was the problem 1. being the TPS sensor, 2. IAC and 3. maybe a computer module problem. I replaced the TPS and IAC and now I'm stuck on 3000rpm and can't get it to come off of it. I was able to get it back down to 1500rpm by disconnecting my batteries. At this point I have no idea. At normal idle my boat use to run about 700-800ish. I have an appointment with a shop next week that has a diagnostic tool that may be able to help pin point the problem. I was also hoping somebody on the forums may be able to help me pin point the problem. I have to drive 1.5 hours to my nearest merc. shop or should I say they are the nearest to me with a scan tool. Until then, if there are checks I can perform I'm 25minutes from the lake to go see if they work. Funny...I live 25 minutes from the lake, but I have to travel 1.5 hours in the opposite direction to the nearest shop and there is not even a lake in the vicinity of the shop (well 1.5hrs in my direction). Thanks for your help...and again sorry for coming on to this forum with my first post being a PROBLEM.
 

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custom boat lover
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First please do not shift it any more at that rpm or you will have a lot more time on the road then just the first 6 hours of going to the dealer the first time. Also if you have a flusher kit to install on the drive so you can run it on the garden hose you would be better off then going to the lake just to try to get the idel down. Have you tryd unhooking the cable to see if it came down?
 

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Ask the question over at OSO (offshoreonly.com) in the tech section. There are some great 454 gear heads over there, unlike all the 496 **** over here. :p
 

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Discussion Starter · #5 ·
First please do not shift it any more at that rpm or you will have a lot more time on the road then just the first 6 hours of going to the dealer the first time. Also if you have a flusher kit to install on the drive so you can run it on the garden hose you would be better off then going to the lake just to try to get the idel down. Have you tryd unhooking the cable to see if it came down?

Correct I will not try to shift at those RPM's...each time its done it to me I've killed the motor and have gotten towed in. I've tried to get it to idle down with the nose cone, but no luck as of yet. I've also disconnected the throttle linkage and RPM's still sticking. Like I stated earlier, at one time I was able to let the engine sit an hour or so, and I would go to restart and everything would be back to normal. It seems the problem has progressed. Now I can only get it to come down to 1500 and that was by disconnecting the batteries. So the boat is acting as if its possessed. Going from normal idle (700-800ish) to 3000rpm back down to 1500rpm and currently won't come off of 1500.
 

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Hi Dirty, welcome to the boards. Looks like you already changed out the most likely items that could cause this. Take off the air cleaner/flame arrestor and just verify that the throttle blades are in fact closing and not hanging up. Next check would be with a scan tool to check sensor voltages and pressures. Not a whole lot other you can check without it.

Question, has the engine ever back fired?
 

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Discussion Starter · #7 ·
Hi Dirty, welcome to the boards. Looks like you already changed out the most likely items that could cause this. Take off the air cleaner/flame arrestor and just verify that the throttle blades are in fact closing and not hanging up. Next check would be with a scan tool to check sensor voltages and pressures. Not a whole lot other you can check without it.

Question, has the engine ever back fired?
I got my first back fire the other day while I had it hooked to the nose cone and I was throttling (rev-ing) the motor up and down trying to get my RPM's to come down. So yes it did back fire and I hope thats not a bad thing. I will also verify the blades are not hanging up. THanks
 

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You need to check both closed and wot voltage at the IAC. Can't do it without a scan tool though. Also start looking for a vacume leak. Look at where the throttle body connects to the manifold and around the injector nozzles. Listen for hissing. If it backfired through the intake it can push out an injector enough to create a vacume leak as well as a gasket. Other than that a scan tool will be in order. Good luck.;)
 

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The HMFIC
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doesent throttle bodies have a flap in side them that the throttle cable moves??? perhaps that spring is gunked up. maybe some throttle body cleaner and a couple of yanks on the throttle to break it up????
 
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